diff --git a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AbstractMessageListenerContainerSpec.java b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AbstractMessageListenerContainerSpec.java
index 5e5eb31215..d0df0d5229 100644
--- a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AbstractMessageListenerContainerSpec.java
+++ b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AbstractMessageListenerContainerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2022 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -290,7 +290,7 @@ public abstract class AbstractMessageListenerContainerSpec<S extends AbstractMes
 
 	/**
 	 * Set the {@link MessagePropertiesConverter} for this listener container.
-	 * @param messagePropertiesConverter The properties converter.
+	 * @param messagePropertiesConverter the converter for AMQP properties.
 	 * @return the spec.
 	 * @see AbstractMessageListenerContainer#setMessagePropertiesConverter(MessagePropertiesConverter)
 	 */
diff --git a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterDMLCSpec.java b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterDMLCSpec.java
index 5b96a3dde8..214933e876 100644
--- a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterDMLCSpec.java
+++ b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterDMLCSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2020 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -36,7 +36,9 @@ public class AmqpInboundChannelAdapterDMLCSpec
 		super(new DirectMessageListenerContainerSpec(listenerContainer));
 	}
 
-	public AmqpInboundChannelAdapterDMLCSpec configureContainer(Consumer<DirectMessageListenerContainerSpec> configurer) {
+	public AmqpInboundChannelAdapterDMLCSpec configureContainer(
+			Consumer<DirectMessageListenerContainerSpec> configurer) {
+
 		configurer.accept((DirectMessageListenerContainerSpec) this.listenerContainerSpec);
 		return this;
 	}
diff --git a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterSMLCSpec.java b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterSMLCSpec.java
index ae235d4257..17ca1e10e4 100644
--- a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterSMLCSpec.java
+++ b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundChannelAdapterSMLCSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2020 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,7 +37,9 @@ public class AmqpInboundChannelAdapterSMLCSpec
 		super(new SimpleMessageListenerContainerSpec(listenerContainer));
 	}
 
-	public AmqpInboundChannelAdapterSMLCSpec configureContainer(Consumer<SimpleMessageListenerContainerSpec> configurer) {
+	public AmqpInboundChannelAdapterSMLCSpec configureContainer(
+			Consumer<SimpleMessageListenerContainerSpec> configurer) {
+
 		configurer.accept((SimpleMessageListenerContainerSpec) this.listenerContainerSpec);
 		return this;
 	}
diff --git a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/package-info.java b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/package-info.java
index 2a0be6595e..ba6c7c00c9 100644
--- a/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/package-info.java
+++ b/spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/package-info.java
@@ -1,4 +1,5 @@
 /**
  * Provides AMQP Component support for the Java DSL.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.integration.amqp.dsl;
diff --git a/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/dsl/package-info.java b/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/dsl/package-info.java
index 2eaba53889..788490080d 100644
--- a/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/dsl/package-info.java
+++ b/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides Apache Cassandra Components support for the Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.cassandra.dsl;
diff --git a/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/CassandraMessageHandler.java b/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/CassandraMessageHandler.java
index 3f8059d32e..411aa880f7 100644
--- a/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/CassandraMessageHandler.java
+++ b/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/CassandraMessageHandler.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,6 +50,7 @@ import org.springframework.integration.expression.ExpressionUtils;
 import org.springframework.integration.handler.AbstractReplyProducingMessageHandler;
 import org.springframework.integration.handler.ExpressionEvaluatingMessageProcessor;
 import org.springframework.integration.handler.MessageProcessor;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 
@@ -75,6 +76,7 @@ public class CassandraMessageHandler extends AbstractReplyProducingMessageHandle
 	/**
 	 * Prepared statement to use in association with high throughput ingestion.
 	 */
+	@Nullable
 	private String ingestQuery;
 
 	/**
diff --git a/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/package-info.java b/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/package-info.java
index 71c8531c65..32acd1b881 100644
--- a/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/package-info.java
+++ b/spring-integration-cassandra/src/main/java/org/springframework/integration/cassandra/outbound/package-info.java
@@ -1,20 +1,5 @@
-/*
- * Copyright 2022 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
 /**
  * Provides classes supporting Cassandra outbound endpoints.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.integration.cassandra.outbound;
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/config/CorrelationStrategyFactoryBean.java b/spring-integration-core/src/main/java/org/springframework/integration/config/CorrelationStrategyFactoryBean.java
index 8a3afa28b5..1bf3b757d1 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/config/CorrelationStrategyFactoryBean.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/config/CorrelationStrategyFactoryBean.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.integration.aggregator.CorrelationStrategy;
 import org.springframework.integration.aggregator.HeaderAttributeCorrelationStrategy;
 import org.springframework.integration.aggregator.MethodInvokingCorrelationStrategy;
 import org.springframework.integration.util.MessagingAnnotationUtils;
+import org.springframework.lang.NonNull;
 import org.springframework.util.StringUtils;
 
 /**
@@ -75,6 +76,7 @@ public class CorrelationStrategyFactoryBean implements FactoryBean<CorrelationSt
 		}
 	}
 
+	@NonNull
 	@Override
 	public CorrelationStrategy getObject() {
 		return this.strategy;
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/config/ReleaseStrategyFactoryBean.java b/spring-integration-core/src/main/java/org/springframework/integration/config/ReleaseStrategyFactoryBean.java
index 4883e342be..68c2b730b2 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/config/ReleaseStrategyFactoryBean.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/config/ReleaseStrategyFactoryBean.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import org.springframework.integration.aggregator.MethodInvokingReleaseStrategy;
 import org.springframework.integration.aggregator.ReleaseStrategy;
 import org.springframework.integration.aggregator.SimpleSequenceSizeReleaseStrategy;
 import org.springframework.integration.util.MessagingAnnotationUtils;
+import org.springframework.lang.NonNull;
 import org.springframework.util.StringUtils;
 
 /**
@@ -87,6 +88,7 @@ public class ReleaseStrategyFactoryBean implements FactoryBean<ReleaseStrategy>,
 		}
 	}
 
+	@NonNull
 	@Override
 	public ReleaseStrategy getObject() {
 		return this.strategy;
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/context/IntegrationObjectSupport.java b/spring-integration-core/src/main/java/org/springframework/integration/context/IntegrationObjectSupport.java
index 0b737259b9..10ec021d7e 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/context/IntegrationObjectSupport.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/context/IntegrationObjectSupport.java
@@ -98,7 +98,7 @@ public abstract class IntegrationObjectSupport implements BeanNameAware, NamedCo
 	private boolean initialized;
 
 	@Override
-	public final void setBeanName(String beanName) {
+	public final void setBeanName(@Nullable String beanName) {
 		this.beanName = beanName;
 	}
 
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/AggregatorSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/AggregatorSpec.java
index 34a49460f0..dd9dc221f2 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/AggregatorSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/AggregatorSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import org.springframework.integration.aggregator.ExpressionEvaluatingMessageGro
 import org.springframework.integration.aggregator.MessageGroupProcessor;
 import org.springframework.integration.aggregator.MethodInvokingMessageGroupProcessor;
 import org.springframework.integration.store.MessageGroup;
+import org.springframework.lang.Nullable;
 
 /**
  * A {@link CorrelationHandlerSpec} for an {@link AggregatingMessageHandler}.
@@ -65,7 +66,7 @@ public class AggregatorSpec extends CorrelationHandlerSpec<AggregatorSpec, Aggre
 	 * target object must have an {@link org.springframework.integration.annotation.Aggregator} annotation).
 	 * @return the handler spec.
 	 */
-	public AggregatorSpec processor(Object target, String methodName) {
+	public AggregatorSpec processor(Object target, @Nullable String methodName) {
 		return super.processor(target)
 				.outputProcessor(methodName != null
 						? new MethodInvokingMessageGroupProcessor(target, methodName)
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/BaseIntegrationFlowDefinition.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/BaseIntegrationFlowDefinition.java
index a9e9bd6590..21be9fac73 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/BaseIntegrationFlowDefinition.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/BaseIntegrationFlowDefinition.java
@@ -150,7 +150,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	}
 
 	protected B addComponents(Map<Object, String> components) {
-		if (components != null) {
+		if (!CollectionUtils.isEmpty(components)) {
 			this.integrationComponents.putAll(components);
 		}
 		return _this();
@@ -223,7 +223,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param messageChannelName the bean name to use.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B fixedSubscriberChannel(String messageChannelName) {
+	public B fixedSubscriberChannel(@Nullable String messageChannelName) {
 		return channel(new FixedSubscriberChannelPrototype(messageChannelName));
 	}
 
@@ -305,7 +305,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * {@link PublishSubscribeSpec} options including 'subflow' definition.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B publishSubscribeChannel(Executor executor,
+	public B publishSubscribeChannel(@Nullable Executor executor,
 			Consumer<PublishSubscribeSpec> publishSubscribeChannelConfigurer) {
 
 		Assert.notNull(publishSubscribeChannelConfigurer, "'publishSubscribeChannelConfigurer' must not be null");
@@ -411,7 +411,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param wireTapConfigurer the {@link Consumer} to accept options for the {@link WireTap}.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B wireTap(IntegrationFlow flow, Consumer<WireTapSpec> wireTapConfigurer) {
+	public B wireTap(IntegrationFlow flow, @Nullable Consumer<WireTapSpec> wireTapConfigurer) {
 		MessageChannel wireTapChannel = obtainInputChannelFromFlow(flow);
 
 		return wireTap(wireTapChannel, wireTapConfigurer);
@@ -473,7 +473,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param wireTapConfigurer the {@link Consumer} to accept options for the {@link WireTap}.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B wireTap(MessageChannel wireTapChannel, Consumer<WireTapSpec> wireTapConfigurer) {
+	public B wireTap(MessageChannel wireTapChannel, @Nullable Consumer<WireTapSpec> wireTapConfigurer) {
 		WireTapSpec wireTapSpec = new WireTapSpec(wireTapChannel);
 		if (wireTapConfigurer != null) {
 			wireTapConfigurer.accept(wireTapSpec);
@@ -528,7 +528,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see ExpressionCommandMessageProcessor
 	 * @see GenericEndpointSpec
 	 */
-	public B controlBus(Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
+	public B controlBus(@Nullable Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
 		return handle(new ServiceActivatingHandler(new ExpressionCommandMessageProcessor(
 				new ControlBusMethodFilter())), endpointConfigurer);
 	}
@@ -553,7 +553,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see ExpressionEvaluatingTransformer
 	 */
 	public B transform(String expression,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		Assert.hasText(expression, "'expression' must not be empty");
 		return transform(null,
@@ -580,7 +580,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see MethodInvokingTransformer
 	 */
-	public B transform(Object service, String methodName) {
+	public B transform(Object service, @Nullable String methodName) {
 		return transform(service, methodName, null);
 	}
 
@@ -593,8 +593,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see ExpressionEvaluatingTransformer
 	 */
-	public B transform(Object service, String methodName,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+	public B transform(Object service, @Nullable String methodName,
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		MethodInvokingTransformer transformer;
 		if (StringUtils.hasText(methodName)) {
@@ -676,7 +676,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see MethodInvokingTransformer
 	 * @see LambdaMessageProcessor
 	 */
-	public <P, T> B transform(Class<P> expectedType, GenericTransformer<P, T> genericTransformer) {
+	public <P, T> B transform(@Nullable Class<P> expectedType, GenericTransformer<P, T> genericTransformer) {
 		return transform(expectedType, genericTransformer, null);
 	}
 
@@ -716,8 +716,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see LambdaMessageProcessor
 	 * @see GenericEndpointSpec
 	 */
-	public <P, T> B transform(Class<P> expectedType, GenericTransformer<P, T> genericTransformer,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+	public <P, T> B transform(@Nullable Class<P> expectedType, GenericTransformer<P, T> genericTransformer,
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		Assert.notNull(genericTransformer, "'genericTransformer' must not be null");
 		Transformer transformer = genericTransformer instanceof Transformer ? (Transformer) genericTransformer :
@@ -750,7 +750,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see FilterEndpointSpec
 	 */
-	public B filter(String expression, Consumer<FilterEndpointSpec> endpointConfigurer) {
+	public B filter(String expression, @Nullable Consumer<FilterEndpointSpec> endpointConfigurer) {
 		Assert.hasText(expression, "'expression' must not be empty");
 		return filter(null, new ExpressionEvaluatingSelector(expression), endpointConfigurer);
 	}
@@ -774,7 +774,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see MethodInvokingSelector
 	 */
-	public B filter(Object service, String methodName) {
+	public B filter(Object service, @Nullable String methodName) {
 		return filter(service, methodName, null);
 	}
 
@@ -787,7 +787,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see MethodInvokingSelector
 	 */
-	public B filter(Object service, String methodName, Consumer<FilterEndpointSpec> endpointConfigurer) {
+	public B filter(Object service, @Nullable String methodName,
+			@Nullable Consumer<FilterEndpointSpec> endpointConfigurer) {
+
 		MethodInvokingSelector selector =
 				StringUtils.hasText(methodName)
 						? new MethodInvokingSelector(service, methodName)
@@ -826,7 +828,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param endpointConfigurer the {@link Consumer} to provide integration endpoint options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B filter(MessageProcessorSpec<?> messageProcessorSpec, Consumer<FilterEndpointSpec> endpointConfigurer) {
+	public B filter(MessageProcessorSpec<?> messageProcessorSpec,
+			@Nullable Consumer<FilterEndpointSpec> endpointConfigurer) {
+
 		Assert.notNull(messageProcessorSpec, MESSAGE_PROCESSOR_SPEC_MUST_NOT_BE_NULL);
 		MessageProcessor<?> processor = messageProcessorSpec.getObject();
 		return addComponent(processor)
@@ -850,7 +854,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see LambdaMessageProcessor
 	 */
-	public <P> B filter(Class<P> expectedType, GenericSelector<P> genericSelector) {
+	public <P> B filter(@Nullable Class<P> expectedType, GenericSelector<P> genericSelector) {
 		return filter(expectedType, genericSelector, null);
 	}
 
@@ -874,15 +878,15 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see LambdaMessageProcessor
 	 * @see FilterEndpointSpec
 	 */
-	public <P> B filter(Class<P> expectedType, GenericSelector<P> genericSelector,
-			Consumer<FilterEndpointSpec> endpointConfigurer) {
+	public <P> B filter(@Nullable Class<P> expectedType, GenericSelector<P> genericSelector,
+			@Nullable Consumer<FilterEndpointSpec> endpointConfigurer) {
 
 		Assert.notNull(genericSelector, "'genericSelector' must not be null");
 		MessageSelector selector = genericSelector instanceof MessageSelector ? (MessageSelector) genericSelector :
 				(ClassUtils.isLambda(genericSelector.getClass())
 						? new MethodInvokingSelector(new LambdaMessageProcessor(genericSelector, expectedType))
 						: new MethodInvokingSelector(genericSelector, ClassUtils.SELECTOR_ACCEPT_METHOD));
-		return this.register(new FilterEndpointSpec(new MessageFilter(selector)), endpointConfigurer);
+		return register(new FilterEndpointSpec(new MessageFilter(selector)), endpointConfigurer);
 	}
 
 	/**
@@ -926,7 +930,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param methodName the method to invoke.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B handle(String beanName, String methodName) {
+	public B handle(String beanName, @Nullable String methodName) {
 		return handle(beanName, methodName, null);
 	}
 
@@ -940,8 +944,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param endpointConfigurer the {@link Consumer} to provide integration endpoint options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B handle(String beanName, String methodName,
-			Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
+	public B handle(String beanName, @Nullable String methodName,
+			@Nullable Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
+
 		return handle(new ServiceActivatingHandler(new BeanNameMessageProcessor<>(beanName, methodName)),
 				endpointConfigurer);
 	}
@@ -966,7 +971,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param methodName the method to invoke.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B handle(Object service, String methodName) {
+	public B handle(Object service, @Nullable String methodName) {
 		return handle(service, methodName, null);
 	}
 
@@ -980,8 +985,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param endpointConfigurer the {@link Consumer} to provide integration endpoint options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B handle(Object service, String methodName,
-			Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
+	public B handle(Object service, @Nullable String methodName,
+			@Nullable Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
 
 		ServiceActivatingHandler handler;
 		if (StringUtils.hasText(methodName)) {
@@ -1011,7 +1016,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see LambdaMessageProcessor
 	 */
-	public <P> B handle(Class<P> expectedType, GenericHandler<P> handler) {
+	public <P> B handle(@Nullable Class<P> expectedType, GenericHandler<P> handler) {
 		return handle(expectedType, handler, null);
 	}
 
@@ -1035,8 +1040,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see LambdaMessageProcessor
 	 */
-	public <P> B handle(Class<P> expectedType, GenericHandler<P> handler,
-			Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
+	public <P> B handle(@Nullable Class<P> expectedType, GenericHandler<P> handler,
+			@Nullable Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
 
 		ServiceActivatingHandler serviceActivatingHandler;
 		if (ClassUtils.isLambda(handler.getClass())) {
@@ -1108,7 +1113,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
 	public <H extends MessageHandler> B handle(MessageHandlerSpec<?, H> messageHandlerSpec,
-			Consumer<GenericEndpointSpec<H>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<H>> endpointConfigurer) {
 
 		Assert.notNull(messageHandlerSpec, "'messageHandlerSpec' must not be null");
 		if (messageHandlerSpec instanceof ComponentsRegistration) {
@@ -1132,7 +1137,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param <H> the {@link MessageHandler} type.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public <H extends MessageHandler> B handle(H messageHandler, Consumer<GenericEndpointSpec<H>> endpointConfigurer) {
+	public <H extends MessageHandler> B handle(H messageHandler,
+			@Nullable Consumer<GenericEndpointSpec<H>> endpointConfigurer) {
+
 		Assert.notNull(messageHandler, "'messageHandler' must not be null");
 		return register(new GenericEndpointSpec<>(messageHandler), endpointConfigurer);
 	}
@@ -1160,7 +1167,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see GenericEndpointSpec
 	 */
-	public B bridge(Consumer<GenericEndpointSpec<BridgeHandler>> endpointConfigurer) {
+	public B bridge(@Nullable Consumer<GenericEndpointSpec<BridgeHandler>> endpointConfigurer) {
 		return handle(new BridgeHandler(), endpointConfigurer);
 	}
 
@@ -1172,7 +1179,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
 	public B delay(String groupId) {
-		return this.delay(groupId, null);
+		return delay(groupId, null);
 	}
 
 	/**
@@ -1183,7 +1190,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see DelayerEndpointSpec
 	 */
-	public B delay(String groupId, Consumer<DelayerEndpointSpec> endpointConfigurer) {
+	public B delay(String groupId, @Nullable Consumer<DelayerEndpointSpec> endpointConfigurer) {
 		return register(new DelayerEndpointSpec(new DelayHandler(groupId)), endpointConfigurer);
 	}
 
@@ -1251,7 +1258,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see GenericEndpointSpec
 	 */
 	public B enrichHeaders(MapBuilder<?, String, Object> headers,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		return enrichHeaders(headers.get(), endpointConfigurer);
 	}
@@ -1279,7 +1286,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see GenericEndpointSpec
 	 */
 	public B enrichHeaders(Map<String, Object> headers,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		HeaderEnricherSpec headerEnricherSpec = new HeaderEnricherSpec();
 		headerEnricherSpec.headers(headers);
@@ -1331,7 +1338,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see SplitterEndpointSpec
 	 */
-	public B split(Consumer<SplitterEndpointSpec<DefaultMessageSplitter>> endpointConfigurer) {
+	public B split(@Nullable Consumer<SplitterEndpointSpec<DefaultMessageSplitter>> endpointConfigurer) {
 		return split(new DefaultMessageSplitter(), endpointConfigurer);
 	}
 
@@ -1354,7 +1361,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see SplitterEndpointSpec
 	 */
-	public B split(String expression, Consumer<SplitterEndpointSpec<ExpressionEvaluatingSplitter>> endpointConfigurer) {
+	public B split(String expression,
+			@Nullable Consumer<SplitterEndpointSpec<ExpressionEvaluatingSplitter>> endpointConfigurer) {
+
 		Assert.hasText(expression, "'expression' must not be empty");
 		return split(new ExpressionEvaluatingSplitter(PARSER.parseExpression(expression)), endpointConfigurer);
 	}
@@ -1378,7 +1387,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see MethodInvokingSplitter
 	 */
-	public B split(Object service, String methodName) {
+	public B split(Object service, @Nullable String methodName) {
 		return split(service, methodName, null);
 	}
 
@@ -1394,8 +1403,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see SplitterEndpointSpec
 	 * @see MethodInvokingSplitter
 	 */
-	public B split(Object service, String methodName,
-			Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
+	public B split(Object service, @Nullable String methodName,
+			@Nullable Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
 
 		MethodInvokingSplitter splitter;
 		if (StringUtils.hasText(methodName)) {
@@ -1414,7 +1423,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param methodName the method to invoke at runtime.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B split(String beanName, String methodName) {
+	public B split(String beanName, @Nullable String methodName) {
 		return split(beanName, methodName, null);
 	}
 
@@ -1429,8 +1438,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see SplitterEndpointSpec
 	 */
-	public B split(String beanName, String methodName,
-			Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
+	public B split(String beanName, @Nullable String methodName,
+			@Nullable Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
 
 		return split(new MethodInvokingSplitter(new BeanNameMessageProcessor<>(beanName, methodName)),
 				endpointConfigurer);
@@ -1471,7 +1480,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see SplitterEndpointSpec
 	 */
 	public B split(MessageProcessorSpec<?> messageProcessorSpec,
-			Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
+			@Nullable Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
 
 		Assert.notNull(messageProcessorSpec, MESSAGE_PROCESSOR_SPEC_MUST_NOT_BE_NULL);
 		MessageProcessor<?> processor = messageProcessorSpec.getObject();
@@ -1531,8 +1540,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see LambdaMessageProcessor
 	 * @see SplitterEndpointSpec
 	 */
-	public <P> B split(Class<P> expectedType, Function<P, ?> splitter,
-			Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
+	public <P> B split(@Nullable Class<P> expectedType, Function<P, ?> splitter,
+			@Nullable Consumer<SplitterEndpointSpec<MethodInvokingSplitter>> endpointConfigurer) {
 
 		MethodInvokingSplitter split =
 				ClassUtils.isLambda(splitter.getClass())
@@ -1563,7 +1572,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see SplitterEndpointSpec
 	 */
 	public <S extends AbstractMessageSplitter> B split(MessageHandlerSpec<?, S> splitterMessageHandlerSpec,
-			Consumer<SplitterEndpointSpec<S>> endpointConfigurer) {
+			@Nullable Consumer<SplitterEndpointSpec<S>> endpointConfigurer) {
+
 		Assert.notNull(splitterMessageHandlerSpec, "'splitterMessageHandlerSpec' must not be null");
 		return split(splitterMessageHandlerSpec.getObject(), endpointConfigurer);
 	}
@@ -1589,7 +1599,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see SplitterEndpointSpec
 	 */
 	public <S extends AbstractMessageSplitter> B split(S splitter,
-			Consumer<SplitterEndpointSpec<S>> endpointConfigurer) {
+			@Nullable Consumer<SplitterEndpointSpec<S>> endpointConfigurer) {
 
 		Assert.notNull(splitter, "'splitter' must not be null");
 		return register(new SplitterEndpointSpec<>(splitter), endpointConfigurer);
@@ -1627,7 +1637,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see GenericEndpointSpec
 	 */
 	public B headerFilter(HeaderFilter headerFilter,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		return transform(null, headerFilter, endpointConfigurer);
 	}
@@ -1639,7 +1649,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
 	public B claimCheckIn(MessageStore messageStore) {
-		return this.claimCheckIn(messageStore, null);
+		return claimCheckIn(messageStore, null);
 	}
 
 	/**
@@ -1652,7 +1662,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see GenericEndpointSpec
 	 */
 	public B claimCheckIn(MessageStore messageStore,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		return transform(null, new ClaimCheckInTransformer(messageStore), endpointConfigurer);
 	}
@@ -1692,7 +1702,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see ClaimCheckOutTransformer#setRemoveMessage(boolean)
 	 */
 	public B claimCheckOut(MessageStore messageStore, boolean removeMessage,
-			Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<MessageTransformingHandler>> endpointConfigurer) {
 
 		ClaimCheckOutTransformer claimCheckOutTransformer = new ClaimCheckOutTransformer(messageStore);
 		claimCheckOutTransformer.setRemoveMessage(removeMessage);
@@ -1727,7 +1737,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see ResequencerSpec
 	 */
-	public B resequence(Consumer<ResequencerSpec> resequencer) {
+	public B resequence(@Nullable Consumer<ResequencerSpec> resequencer) {
 		return register(new ResequencerSpec(), resequencer);
 	}
 
@@ -1765,7 +1775,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see AggregatorSpec
 	 */
-	public B aggregate(Consumer<AggregatorSpec> aggregator) {
+	public B aggregate(@Nullable Consumer<AggregatorSpec> aggregator) {
 		return register(new AggregatorSpec(), aggregator);
 	}
 
@@ -1776,7 +1786,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param method the method to invoke at runtime.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B route(String beanName, String method) {
+	public B route(String beanName, @Nullable String method) {
 		return route(beanName, method, null);
 	}
 
@@ -1788,8 +1798,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param routerConfigurer the {@link Consumer} to provide {@link MethodInvokingRouter} options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B route(String beanName, String method, Consumer<RouterSpec<Object,
-			MethodInvokingRouter>> routerConfigurer) {
+	public B route(String beanName, @Nullable String method,
+			@Nullable Consumer<RouterSpec<Object, MethodInvokingRouter>> routerConfigurer) {
 
 		MethodInvokingRouter methodInvokingRouter =
 				new MethodInvokingRouter(new BeanNameMessageProcessor<>(beanName, method));
@@ -1815,7 +1825,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see MethodInvokingRouter
 	 */
-	public B route(Object service, String methodName) {
+	public B route(Object service, @Nullable String methodName) {
 		return route(service, methodName, null);
 	}
 
@@ -1828,8 +1838,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see MethodInvokingRouter
 	 */
-	public B route(Object service, String methodName,
-			Consumer<RouterSpec<Object, MethodInvokingRouter>> routerConfigurer) {
+	public B route(Object service, @Nullable String methodName,
+			@Nullable Consumer<RouterSpec<Object, MethodInvokingRouter>> routerConfigurer) {
 
 		MethodInvokingRouter router;
 		if (StringUtils.hasText(methodName)) {
@@ -1859,7 +1869,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param <T> the target result type.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public <T> B route(String expression, Consumer<RouterSpec<T, ExpressionEvaluatingRouter>> routerConfigurer) {
+	public <T> B route(String expression,
+			@Nullable Consumer<RouterSpec<T, ExpressionEvaluatingRouter>> routerConfigurer) {
+
 		return route(new RouterSpec<>(new ExpressionEvaluatingRouter(PARSER.parseExpression(expression))),
 				routerConfigurer);
 	}
@@ -1882,7 +1894,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see LambdaMessageProcessor
 	 */
-	public <S, T> B route(Class<S> expectedType, Function<S, T> router) {
+	public <S, T> B route(@Nullable Class<S> expectedType, Function<S, T> router) {
 		return route(expectedType, router, null);
 	}
 
@@ -1910,8 +1922,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see LambdaMessageProcessor
 	 */
-	public <P, T> B route(Class<P> expectedType, Function<P, T> router,
-			Consumer<RouterSpec<T, MethodInvokingRouter>> routerConfigurer) {
+	public <P, T> B route(@Nullable Class<P> expectedType, Function<P, T> router,
+			@Nullable Consumer<RouterSpec<T, MethodInvokingRouter>> routerConfigurer) {
 
 		MethodInvokingRouter methodInvokingRouter =
 				ClassUtils.isLambda(router.getClass())
@@ -1953,7 +1965,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
 	public B route(MessageProcessorSpec<?> messageProcessorSpec,
-			Consumer<RouterSpec<Object, MethodInvokingRouter>> routerConfigurer) {
+			@Nullable Consumer<RouterSpec<Object, MethodInvokingRouter>> routerConfigurer) {
 
 		Assert.notNull(messageProcessorSpec, MESSAGE_PROCESSOR_SPEC_MUST_NOT_BE_NULL);
 		MessageProcessor<?> processor = messageProcessorSpec.getObject();
@@ -1963,7 +1975,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	}
 
 	protected <R extends AbstractMessageRouter, S extends AbstractRouterSpec<? super S, R>> B route(S routerSpec,
-			Consumer<S> routerConfigurer) {
+			@Nullable Consumer<S> routerConfigurer) {
 
 		if (routerConfigurer != null) {
 			routerConfigurer.accept(routerSpec);
@@ -1974,7 +1986,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 
 		Map<Object, String> componentsToRegister = null;
 		Map<Object, String> routerComponents = routerSpec.getComponentsToRegister();
-		if (routerComponents != null) {
+		if (!CollectionUtils.isEmpty(routerComponents)) {
 			componentsToRegister = new LinkedHashMap<>(routerComponents);
 			routerComponents.clear();
 		}
@@ -2069,7 +2081,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param <R> the {@link AbstractMessageRouter} type.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public <R extends AbstractMessageRouter> B route(R router, Consumer<GenericEndpointSpec<R>> endpointConfigurer) {
+	public <R extends AbstractMessageRouter> B route(R router,
+			@Nullable Consumer<GenericEndpointSpec<R>> endpointConfigurer) {
+
 		return handle(router, endpointConfigurer);
 	}
 
@@ -2098,7 +2112,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B gateway(String requestChannel, Consumer<GatewayEndpointSpec> endpointConfigurer) {
+	public B gateway(String requestChannel, @Nullable Consumer<GatewayEndpointSpec> endpointConfigurer) {
 		return register(new GatewayEndpointSpec(requestChannel), endpointConfigurer);
 	}
 
@@ -2127,7 +2141,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B gateway(MessageChannel requestChannel, Consumer<GatewayEndpointSpec> endpointConfigurer) {
+	public B gateway(MessageChannel requestChannel, @Nullable Consumer<GatewayEndpointSpec> endpointConfigurer) {
 		return register(new GatewayEndpointSpec(requestChannel), endpointConfigurer);
 	}
 
@@ -2162,7 +2176,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @param endpointConfigurer the {@link Consumer} to provide integration endpoint options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B gateway(IntegrationFlow flow, Consumer<GatewayEndpointSpec> endpointConfigurer) {
+	public B gateway(IntegrationFlow flow, @Nullable Consumer<GatewayEndpointSpec> endpointConfigurer) {
 		MessageChannel requestChannel = obtainInputChannelFromFlow(flow);
 		return gateway(requestChannel, endpointConfigurer);
 	}
@@ -2217,7 +2231,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see #wireTap(WireTapSpec)
 	 */
-	public B log(LoggingHandler.Level level, String category) {
+	public B log(LoggingHandler.Level level, @Nullable String category) {
 		return log(level, category, (Expression) null);
 	}
 
@@ -2365,7 +2379,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 * @see #wireTap(WireTapSpec)
 	 */
-	public B log(LoggingHandler.Level level, String category, Expression logExpression) {
+	public B log(LoggingHandler.Level level, @Nullable String category, @Nullable Expression logExpression) {
 		LoggingHandler loggingHandler = new LoggingHandler(level);
 		if (StringUtils.hasText(category)) {
 			loggingHandler.setLoggerName(category);
@@ -2457,7 +2471,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see #bridge()
 	 */
 	@Deprecated
-	public IntegrationFlow logAndReply(LoggingHandler.Level level, String category) {
+	public IntegrationFlow logAndReply(LoggingHandler.Level level, @Nullable String category) {
 		return logAndReply(level, category, (Expression) null);
 	}
 
@@ -2661,7 +2675,9 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @see #bridge()
 	 */
 	@Deprecated
-	public IntegrationFlow logAndReply(LoggingHandler.Level level, String category, Expression logExpression) {
+	public IntegrationFlow logAndReply(LoggingHandler.Level level, @Nullable String category,
+			@Nullable Expression logExpression) {
+
 		return log(level, category, logExpression)
 				.bridge()
 				.get();
@@ -2687,7 +2703,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * Can be {@code null}.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B scatterGather(MessageChannel scatterChannel, Consumer<AggregatorSpec> gatherer) {
+	public B scatterGather(MessageChannel scatterChannel, @Nullable Consumer<AggregatorSpec> gatherer) {
 		return scatterGather(scatterChannel, gatherer, null);
 	}
 
@@ -2702,8 +2718,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * {@link ScatterGatherHandler} and its endpoint. Can be {@code null}.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B scatterGather(MessageChannel scatterChannel, Consumer<AggregatorSpec> gatherer,
-			Consumer<ScatterGatherSpec> scatterGather) {
+	public B scatterGather(MessageChannel scatterChannel, @Nullable Consumer<AggregatorSpec> gatherer,
+			@Nullable Consumer<ScatterGatherSpec> scatterGather) {
 
 		AggregatorSpec aggregatorSpec = new AggregatorSpec();
 		if (gatherer != null) {
@@ -2790,7 +2806,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * {@link org.springframework.integration.aggregator.BarrierMessageHandler} options.
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
-	public B barrier(long timeout, Consumer<BarrierSpec> barrierConfigurer) {
+	public B barrier(long timeout, @Nullable Consumer<BarrierSpec> barrierConfigurer) {
 		return register(new BarrierSpec(timeout), barrierConfigurer);
 	}
 
@@ -2811,7 +2827,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
 	public B trigger(String triggerActionId,
-			Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
 
 		MessageProcessor<Void> trigger = new BeanNameMessageProcessor<>(triggerActionId, "trigger");
 		return handle(new ServiceActivatingHandler(trigger), endpointConfigurer);
@@ -2834,7 +2850,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	 * @return the current {@link BaseIntegrationFlowDefinition}.
 	 */
 	public B trigger(MessageTriggerAction triggerAction,
-			Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
+			@Nullable Consumer<GenericEndpointSpec<ServiceActivatingHandler>> endpointConfigurer) {
 
 		Consumer<Message<?>> trigger = triggerAction::trigger;
 		return handle(new ServiceActivatingHandler(new LambdaMessageProcessor(trigger, Message.class)),
@@ -2959,7 +2975,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 	}
 
 	protected <S extends ConsumerEndpointSpec<? super S, ? extends MessageHandler>> B register(S endpointSpec,
-			Consumer<S> endpointConfigurer) {
+			@Nullable Consumer<S> endpointConfigurer) {
 
 		if (endpointConfigurer != null) {
 			endpointConfigurer.accept(endpointSpec);
@@ -2977,7 +2993,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 		addComponents(endpointSpec.getComponentsToRegister());
 
 		if (inputChannel instanceof MessageChannelReference messageChannelReference) {
-			factoryBeanTuple2.getT1().setInputChannelName(messageChannelReference.getName());
+			factoryBeanTuple2.getT1().setInputChannelName(messageChannelReference.name());
 		}
 		else {
 			if (inputChannel instanceof FixedSubscriberChannelPrototype fixedSubscriberChannel) {
@@ -3001,7 +3017,7 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 			if (currComponent != null) {
 				String channelName = null;
 				if (outputChannel instanceof MessageChannelReference channelReference) {
-					channelName = channelReference.getName();
+					channelName = channelReference.name();
 				}
 
 				if (currComponent instanceof MessageProducer messageProducer) {
@@ -3099,7 +3115,8 @@ public abstract class BaseIntegrationFlowDefinition<B extends BaseIntegrationFlo
 		REFERENCED_REPLY_PRODUCERS.add(replyHandler);
 	}
 
-	protected static Object extractProxyTarget(Object target) {
+	@Nullable
+	protected static Object extractProxyTarget(@Nullable Object target) {
 		if (!(target instanceof Advised advised)) {
 			return target;
 		}
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/ConsumerEndpointSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/ConsumerEndpointSpec.java
index ed6566b256..61c4cecf49 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/ConsumerEndpointSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/ConsumerEndpointSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -38,6 +38,7 @@ import org.springframework.integration.handler.advice.ReactiveRequestHandlerAdvi
 import org.springframework.integration.router.AbstractMessageRouter;
 import org.springframework.integration.scheduling.PollerMetadata;
 import org.springframework.integration.transaction.TransactionInterceptorBuilder;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHandler;
 import org.springframework.scheduling.TaskScheduler;
@@ -61,7 +62,7 @@ public abstract class ConsumerEndpointSpec<S extends ConsumerEndpointSpec<S, H>,
 
 	protected final List<Advice> adviceChain = new LinkedList<>(); // NOSONAR final
 
-	protected ConsumerEndpointSpec(H messageHandler) {
+	protected ConsumerEndpointSpec(@Nullable H messageHandler) {
 		super(messageHandler, new ConsumerEndpointFactoryBean());
 	}
 
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/EndpointSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/EndpointSpec.java
index ca86c24a06..742c78a5f9 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/EndpointSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/EndpointSpec.java
@@ -28,6 +28,7 @@ import org.springframework.beans.factory.FactoryBean;
 import org.springframework.integration.channel.DirectChannel;
 import org.springframework.integration.endpoint.AbstractEndpoint;
 import org.springframework.integration.scheduling.PollerMetadata;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.util.Assert;
 
@@ -54,7 +55,7 @@ public abstract class EndpointSpec<S extends EndpointSpec<S, F, H>, F extends Be
 
 	protected H handler; // NOSONAR
 
-	protected EndpointSpec(H handler, F endpointFactoryBean) {
+	protected EndpointSpec(@Nullable H handler, F endpointFactoryBean) {
 		this.endpointFactoryBean = endpointFactoryBean;
 		this.handler = handler;
 	}
@@ -83,9 +84,7 @@ public abstract class EndpointSpec<S extends EndpointSpec<S, F, H>, F extends Be
 	 */
 	public S poller(PollerSpec pollerMetadataSpec) {
 		Map<Object, String> components = pollerMetadataSpec.getComponentsToRegister();
-		if (components != null) {
-			this.componentsToRegister.putAll(components);
-		}
+		this.componentsToRegister.putAll(components);
 		return poller(pollerMetadataSpec.getObject());
 	}
 
@@ -122,9 +121,7 @@ public abstract class EndpointSpec<S extends EndpointSpec<S, F, H>, F extends Be
 
 	@Override
 	public Map<Object, String> getComponentsToRegister() {
-		return this.componentsToRegister.isEmpty()
-				? null
-				: this.componentsToRegister;
+		return this.componentsToRegister;
 	}
 
 	@Override
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/EnricherSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/EnricherSpec.java
index 8bc1d7baf9..7a8ed03808 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/EnricherSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/EnricherSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,7 @@ import org.springframework.integration.transformer.support.AbstractHeaderValueMe
 import org.springframework.integration.transformer.support.ExpressionEvaluatingHeaderValueMessageProcessor;
 import org.springframework.integration.transformer.support.HeaderValueMessageProcessor;
 import org.springframework.integration.transformer.support.StaticHeaderValueMessageProcessor;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.util.Assert;
@@ -235,7 +236,7 @@ public class EnricherSpec extends ConsumerEndpointSpec<EnricherSpec, ContentEnri
 	 * @return the enricher spec.
 	 * @see ContentEnricher#setHeaderExpressions(Map)
 	 */
-	public <V> EnricherSpec header(String name, V value, Boolean overwrite) {
+	public <V> EnricherSpec header(String name, V value, @Nullable Boolean overwrite) {
 		AbstractHeaderValueMessageProcessor<V> headerValueMessageProcessor =
 				new StaticHeaderValueMessageProcessor<V>(value);
 		headerValueMessageProcessor.setOverwrite(overwrite);
@@ -260,7 +261,7 @@ public class EnricherSpec extends ConsumerEndpointSpec<EnricherSpec, ContentEnri
 	 * @return the enricher spec.
 	 * @see ContentEnricher#setHeaderExpressions(Map)
 	 */
-	public EnricherSpec headerExpression(String name, String expression, Boolean overwrite) {
+	public EnricherSpec headerExpression(String name, String expression, @Nullable Boolean overwrite) {
 		Assert.hasText(expression, "'expression' must not be empty");
 		return headerExpression(name, PARSER.parseExpression(expression), overwrite);
 	}
@@ -287,11 +288,13 @@ public class EnricherSpec extends ConsumerEndpointSpec<EnricherSpec, ContentEnri
 	 * @see ContentEnricher#setHeaderExpressions(Map)
 	 * @see FunctionExpression
 	 */
-	public <P> EnricherSpec headerFunction(String name, Function<Message<P>, Object> function, Boolean overwrite) {
+	public <P> EnricherSpec headerFunction(String name, Function<Message<P>, Object> function,
+			@Nullable Boolean overwrite) {
+
 		return headerExpression(name, new FunctionExpression<>(function), overwrite);
 	}
 
-	private EnricherSpec headerExpression(String name, Expression expression, Boolean overwrite) {
+	private EnricherSpec headerExpression(String name, Expression expression, @Nullable Boolean overwrite) {
 		AbstractHeaderValueMessageProcessor<?> headerValueMessageProcessor =
 				new ExpressionEvaluatingHeaderValueMessageProcessor<>(expression, null);
 		headerValueMessageProcessor.setOverwrite(overwrite);
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/HeaderEnricherSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/HeaderEnricherSpec.java
index 1495837514..240286afc8 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/HeaderEnricherSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/HeaderEnricherSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -41,6 +41,7 @@ import org.springframework.integration.transformer.support.ExpressionEvaluatingH
 import org.springframework.integration.transformer.support.HeaderValueMessageProcessor;
 import org.springframework.integration.transformer.support.RoutingSlipHeaderValueMessageProcessor;
 import org.springframework.integration.transformer.support.StaticHeaderValueMessageProcessor;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHeaders;
 import org.springframework.util.Assert;
@@ -133,7 +134,7 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	/**
 	 * Add header specifications from the {@link MapBuilder}; if a map value is an
 	 * {@link Expression}, it will be evaluated at run time when the message headers are
-	 * enriched. Otherwise the value is simply added to the headers. Headers derived from
+	 * enriched. Otherwise, the value is simply added to the headers. Headers derived from
 	 * the map will <b>not</b> overwrite existing headers, unless
 	 * {@link #defaultOverwrite(boolean)} is true.
 	 * @param headers the header map builder.
@@ -146,12 +147,12 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	/**
 	 * Add header specifications from the {@link MapBuilder}; if a map value is an
 	 * {@link Expression}, it will be evaluated at run time when the message headers are
-	 * enriched. Otherwise the value is simply added to the headers.
+	 * enriched. Otherwise, the value is simply added to the headers.
 	 * @param headers the header map builder.
 	 * @param overwrite true to overwrite existing headers.
 	 * @return the header enricher spec.
 	 */
-	public HeaderEnricherSpec headers(MapBuilder<?, String, Object> headers, Boolean overwrite) {
+	public HeaderEnricherSpec headers(MapBuilder<?, String, Object> headers, @Nullable Boolean overwrite) {
 		Assert.notNull(headers, HEADERS_MUST_NOT_BE_NULL);
 		return headers(headers.get(), overwrite);
 	}
@@ -159,7 +160,7 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	/**
 	 * Add header specifications from the {@link Map}; if a map value is an
 	 * {@link Expression}, it will be evaluated at run time when the message headers are
-	 * enriched. Otherwise the value is simply added to the headers. Headers derived from
+	 * enriched. Otherwise, the value is simply added to the headers. Headers derived from
 	 * the map will <em>not</em> overwrite existing headers, unless
 	 * {@link #defaultOverwrite(boolean)} is true.
 	 * @param headers The header builder.
@@ -172,12 +173,12 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	/**
 	 * Add header specifications from the {@link Map}; if a map value is an
 	 * {@link Expression}, it will be evaluated at run time when the message headers are
-	 * enriched. Otherwise the value is simply added to the headers.
+	 * enriched. Otherwise, the value is simply added to the headers.
 	 * @param headers The header builder.
 	 * @param overwrite true to overwrite existing headers.
 	 * @return the header enricher spec.
 	 */
-	public HeaderEnricherSpec headers(Map<String, Object> headers, Boolean overwrite) {
+	public HeaderEnricherSpec headers(Map<String, Object> headers, @Nullable Boolean overwrite) {
 		Assert.notNull(headers, HEADERS_MUST_NOT_BE_NULL);
 		for (Entry<String, Object> entry : headers.entrySet()) {
 			String name = entry.getKey();
@@ -753,7 +754,7 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	 * @param <V> the value type.
 	 * @return the header enricher spec.
 	 */
-	public <V> HeaderEnricherSpec header(String name, V value, Boolean overwrite) {
+	public <V> HeaderEnricherSpec header(String name, V value, @Nullable Boolean overwrite) {
 		AbstractHeaderValueMessageProcessor<V> headerValueMessageProcessor =
 				new StaticHeaderValueMessageProcessor<>(value);
 		headerValueMessageProcessor.setOverwrite(overwrite);
@@ -780,7 +781,7 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	 * @param overwrite true to overwrite an existing header.
 	 * @return the header enricher spec.
 	 */
-	public HeaderEnricherSpec headerExpression(String name, String expression, Boolean overwrite) {
+	public HeaderEnricherSpec headerExpression(String name, String expression, @Nullable Boolean overwrite) {
 		Assert.hasText(expression, "'expression' must not be empty");
 		return headerExpression(name, PARSER.parseExpression(expression), overwrite);
 	}
@@ -810,12 +811,12 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	 * @see FunctionExpression
 	 */
 	public <P> HeaderEnricherSpec headerFunction(String name, Function<Message<P>, ?> function,
-			Boolean overwrite) {
+			@Nullable Boolean overwrite) {
 
 		return headerExpression(name, new FunctionExpression<>(function), overwrite);
 	}
 
-	private HeaderEnricherSpec headerExpression(String name, Expression expression, Boolean overwrite) {
+	private HeaderEnricherSpec headerExpression(String name, Expression expression, @Nullable Boolean overwrite) {
 		AbstractHeaderValueMessageProcessor<?> headerValueMessageProcessor =
 				new ExpressionEvaluatingHeaderValueMessageProcessor<>(expression, null);
 		headerValueMessageProcessor.setOverwrite(overwrite);
@@ -859,7 +860,7 @@ public class HeaderEnricherSpec extends ConsumerEndpointSpec<HeaderEnricherSpec,
 	 * @return the header enricher spec.
 	 * @see org.springframework.integration.support.channel.HeaderChannelRegistry
 	 */
-	public HeaderEnricherSpec headerChannelsToString(String timeToLiveExpression) {
+	public HeaderEnricherSpec headerChannelsToString(@Nullable String timeToLiveExpression) {
 		return headerExpression("replyChannel",
 				"@" + IntegrationContextUtils.INTEGRATION_HEADER_CHANNEL_REGISTRY_BEAN_NAME
 						+ ".channelToChannelName(headers.replyChannel" +
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationComponentSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationComponentSpec.java
index 5337dca13f..a7cb9fd638 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationComponentSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationComponentSpec.java
@@ -26,6 +26,8 @@ import org.springframework.beans.factory.InitializingBean;
 import org.springframework.context.Lifecycle;
 import org.springframework.context.SmartLifecycle;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
+import org.springframework.lang.NonNull;
+import org.springframework.lang.Nullable;
 
 /**
  * The common Builder abstraction.
@@ -57,11 +59,12 @@ public abstract class IntegrationComponentSpec<S extends IntegrationComponentSpe
 	 * @param idToSet the id.
 	 * @return the spec.
 	 */
-	protected S id(String idToSet) {
+	protected S id(@Nullable String idToSet) {
 		this.id = idToSet;
 		return _this();
 	}
 
+	@Nullable
 	public final String getId() {
 		return this.id;
 	}
@@ -85,6 +88,7 @@ public abstract class IntegrationComponentSpec<S extends IntegrationComponentSpe
 	 * !!! This method must not be called from the target configuration !!!
 	 * @return the object backed by this factory bean.
 	 */
+	@NonNull
 	@Override
 	public T getObject() {
 		if (this.target == null) {
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlow.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlow.java
index f776d82d41..f02c571a01 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlow.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlow.java
@@ -16,6 +16,7 @@
 
 package org.springframework.integration.dsl;
 
+import java.util.Collections;
 import java.util.Map;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
@@ -114,6 +115,7 @@ public interface IntegrationFlow {
 	 * @return the channel.
 	 * @since 5.0.4
 	 */
+	@Nullable
 	default MessageChannel getInputChannel() {
 		return null;
 	}
@@ -124,7 +126,7 @@ public interface IntegrationFlow {
 	 * @since 5.5.4
 	 */
 	default Map<Object, String> getIntegrationComponents() {
-		return null;
+		return Collections.emptyMap();
 	}
 
 	/**
@@ -214,7 +216,7 @@ public interface IntegrationFlow {
 	 * @see SourcePollingChannelAdapterSpec
 	 */
 	static IntegrationFlowBuilder from(MessageSourceSpec<?, ? extends MessageSource<?>> messageSourceSpec,
-			Consumer<SourcePollingChannelAdapterSpec> endpointConfigurer) {
+			@Nullable Consumer<SourcePollingChannelAdapterSpec> endpointConfigurer) {
 
 		Assert.notNull(messageSourceSpec, "'messageSourceSpec' must not be null");
 		return from(messageSourceSpec.getObject(), endpointConfigurer, registerComponents(messageSourceSpec));
@@ -246,7 +248,7 @@ public interface IntegrationFlow {
 	 * @see Supplier
 	 */
 	static <T> IntegrationFlowBuilder fromSupplier(Supplier<T> messageSource,
-			Consumer<SourcePollingChannelAdapterSpec> endpointConfigurer) {
+			@Nullable Consumer<SourcePollingChannelAdapterSpec> endpointConfigurer) {
 
 		Assert.notNull(messageSource, "'messageSource' must not be null");
 		return from(new AbstractMessageSource<>() {
@@ -440,7 +442,7 @@ public interface IntegrationFlow {
 	@SuppressWarnings("overloads")
 	static IntegrationFlowBuilder from(IntegrationFlow other) {
 		Map<Object, String> integrationComponents = other.getIntegrationComponents();
-		Assert.notNull(integrationComponents, () ->
+		Assert.notEmpty(integrationComponents, () ->
 				"The provided integration flow to compose from '" + other +
 						"' must be declared as a bean in the application context");
 		Object lastIntegrationComponentFromOther =
@@ -488,6 +490,7 @@ public interface IntegrationFlow {
 		return integrationFlowBuilder.addComponent(inboundGateway);
 	}
 
+	@Nullable
 	private static IntegrationFlowBuilder registerComponents(Object spec) {
 		if (spec instanceof ComponentsRegistration componentsRegistration) {
 			return new IntegrationFlowBuilder()
@@ -496,8 +499,9 @@ public interface IntegrationFlow {
 		return null;
 	}
 
+	@Nullable
 	@SuppressWarnings("unchecked")
-	private static <T> T extractProxyTarget(T target) {
+	private static <T> T extractProxyTarget(@Nullable T target) {
 		if (!(target instanceof Advised advised)) {
 			return target;
 		}
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowAdapter.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowAdapter.java
index e9cbbfda14..1b30df054e 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowAdapter.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowAdapter.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,7 +37,7 @@ import org.springframework.util.Assert;
  * Requires the implementation for the {@link #buildFlow()} method to produce
  * {@link IntegrationFlowDefinition} using one of {@link #from} support methods.
  * <p>
- * Typically is used for target service implementation:
+ * Typically, is used for target service implementation:
  * <pre class="code">
  *  &#64;Component
  *  public class MyFlowAdapter extends IntegrationFlowAdapter {
@@ -68,12 +68,12 @@ public abstract class IntegrationFlowAdapter implements IntegrationFlow, Managea
 	@Override
 	public final void configure(IntegrationFlowDefinition<?> flow) {
 		IntegrationFlowDefinition<?> targetFlow = buildFlow();
-		Assert.state(targetFlow != null, "the 'buildFlow()' must not return null");
 		flow.integrationComponents.clear();
 		flow.integrationComponents.putAll(targetFlow.integrationComponents);
 		this.targetIntegrationFlow = flow.get();
 	}
 
+	@Nullable
 	@Override
 	public MessageChannel getInputChannel() {
 		assertTargetIntegrationFlow();
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowDefinition.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowDefinition.java
index c1ab2e05a9..de2ce2ca78 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowDefinition.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowDefinition.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -64,7 +64,7 @@ public abstract class IntegrationFlowDefinition<B extends IntegrationFlowDefinit
 
 	/**
 	 * Populate the {@link MessageTransformingHandler} instance for the provided
-	 * {@link GenericTransformer}. In addition accept options for the integration endpoint
+	 * {@link GenericTransformer}. In addition, accept options for the integration endpoint
 	 * using {@link GenericEndpointSpec}. Use
 	 * {@link #transform(Class, GenericTransformer, Consumer)} if you need to access the
 	 * entire message.
@@ -226,7 +226,7 @@ public abstract class IntegrationFlowDefinition<B extends IntegrationFlowDefinit
 	/**
 	 * Populate the {@link MethodInvokingRouter} for provided {@link Function}
 	 * with provided options from {@link RouterSpec}.
-	 * In addition accept options for the integration endpoint using {@link GenericEndpointSpec}.
+	 * In addition, accept options for the integration endpoint using {@link GenericEndpointSpec}.
 	 * Typically used with a Java 8 Lambda expression:
 	 * <pre class="code">
 	 * {@code
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessageProducerSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessageProducerSpec.java
index 37baf9fd3a..49217f87a6 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessageProducerSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessageProducerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.integration.dsl;
 
 import org.springframework.integration.endpoint.MessageProducerSupport;
 import org.springframework.integration.support.ErrorMessageStrategy;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 
 /**
@@ -34,7 +35,7 @@ import org.springframework.messaging.MessageChannel;
 public abstract class MessageProducerSpec<S extends MessageProducerSpec<S, P>, P extends MessageProducerSupport>
 		extends IntegrationComponentSpec<S, P> {
 
-	public MessageProducerSpec(P producer) {
+	public MessageProducerSpec(@Nullable P producer) {
 		this.target = producer;
 	}
 
@@ -43,7 +44,7 @@ public abstract class MessageProducerSpec<S extends MessageProducerSpec<S, P>, P
 	 * Configure the message producer's bean name.
 	 */
 	@Override
-	public S id(String id) {
+	public S id(@Nullable String id) {
 		this.target.setBeanName(id);
 		return super.id(id);
 	}
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessagingGatewaySpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessagingGatewaySpec.java
index 90b9996346..23915e3265 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessagingGatewaySpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/MessagingGatewaySpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ package org.springframework.integration.dsl;
 import org.springframework.integration.gateway.MessagingGatewaySupport;
 import org.springframework.integration.mapping.InboundMessageMapper;
 import org.springframework.integration.mapping.OutboundMessageMapper;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 
 /**
@@ -34,12 +35,12 @@ import org.springframework.messaging.MessageChannel;
 public abstract class MessagingGatewaySpec<S extends MessagingGatewaySpec<S, G>, G extends MessagingGatewaySupport>
 		extends IntegrationComponentSpec<S, G> {
 
-	public MessagingGatewaySpec(G gateway) {
+	public MessagingGatewaySpec(@Nullable G gateway) {
 		this.target = gateway;
 	}
 
 	@Override
-	public S id(String id) {
+	public S id(@Nullable String id) {
 		this.target.setBeanName(id);
 		return super.id(id);
 	}
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/RecipientListRouterSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/RecipientListRouterSpec.java
index 4c298d9cd7..2f6246c6ae 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/RecipientListRouterSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/RecipientListRouterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import org.springframework.integration.filter.ExpressionEvaluatingSelector;
 import org.springframework.integration.filter.MethodInvokingSelector;
 import org.springframework.integration.router.RecipientListRouter;
 import org.springframework.integration.util.ClassUtils;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.util.StringUtils;
 
@@ -89,7 +90,7 @@ public class RecipientListRouterSpec extends AbstractRouterSpec<RecipientListRou
 	}
 
 	/**
-	 * Adds a recipient channel that will be selected if the the selector's accept method returns 'true'.
+	 * Adds a recipient channel that will be selected if the selector's accept method returns 'true'.
 	 * @param channelName the channel name.
 	 * @param selector the selector.
 	 * @param <P> the selector source type.
@@ -113,7 +114,7 @@ public class RecipientListRouterSpec extends AbstractRouterSpec<RecipientListRou
 	}
 
 	/**
-	 * Adds a recipient channel that always will be selected.
+	 * Adds a recipient channel that always is selected.
 	 * @param channel the recipient channel.
 	 * @return the router spec.
 	 */
@@ -122,22 +123,22 @@ public class RecipientListRouterSpec extends AbstractRouterSpec<RecipientListRou
 	}
 
 	/**
-	 * Adds a recipient channel that will be selected if the the expression evaluates to 'true'.
+	 * Adds a recipient channel that will be selected if the expression evaluates to 'true'.
 	 * @param channel the recipient channel.
 	 * @param expression the expression.
 	 * @return the router spec.
 	 */
-	public RecipientListRouterSpec recipient(MessageChannel channel, String expression) {
+	public RecipientListRouterSpec recipient(MessageChannel channel, @Nullable String expression) {
 		return recipient(channel, StringUtils.hasText(expression) ? PARSER.parseExpression(expression) : null);
 	}
 
 	/**
-	 * Adds a recipient channel that will be selected if the the expression evaluates to 'true'.
+	 * Adds a recipient channel that will be selected if the expression evaluates to 'true'.
 	 * @param channel the recipient channel.
 	 * @param expression the expression.
 	 * @return the router spec.
 	 */
-	public RecipientListRouterSpec recipient(MessageChannel channel, Expression expression) {
+	public RecipientListRouterSpec recipient(MessageChannel channel, @Nullable Expression expression) {
 		if (expression != null) {
 			ExpressionEvaluatingSelector selector = new ExpressionEvaluatingSelector(expression);
 			this.handler.addRecipient(channel, selector);
@@ -150,7 +151,7 @@ public class RecipientListRouterSpec extends AbstractRouterSpec<RecipientListRou
 	}
 
 	/**
-	 * Adds a recipient channel that will be selected if the the selector's accept method returns 'true'.
+	 * Adds a recipient channel that will be selected if the selector's accept method returns 'true'.
 	 * @param channel the recipient channel.
 	 * @param selector the selector.
 	 * @return the router spec.
@@ -160,7 +161,7 @@ public class RecipientListRouterSpec extends AbstractRouterSpec<RecipientListRou
 	}
 
 	/**
-	 * Adds a recipient channel that will be selected if the the selector's accept method returns 'true'.
+	 * Adds a recipient channel that will be selected if the selector's accept method returns 'true'.
 	 * @param channel the recipient channel.
 	 * @param selector the selector.
 	 * @param <P> the selector source type.
@@ -210,7 +211,7 @@ public class RecipientListRouterSpec extends AbstractRouterSpec<RecipientListRou
 	 * @param subFlow the subflow.
 	 * @return the router spec.
 	 */
-	public RecipientListRouterSpec recipientFlow(String expression, IntegrationFlow subFlow) {
+	public RecipientListRouterSpec recipientFlow(@Nullable String expression, IntegrationFlow subFlow) {
 		return recipientFlow(StringUtils.hasText(expression) ? PARSER.parseExpression(expression) : null, subFlow);
 	}
 
@@ -220,7 +221,7 @@ public class RecipientListRouterSpec extends AbstractRouterSpec<RecipientListRou
 	 * @param subFlow the subflow.
 	 * @return the router spec.
 	 */
-	public RecipientListRouterSpec recipientFlow(Expression expression, IntegrationFlow subFlow) {
+	public RecipientListRouterSpec recipientFlow(@Nullable Expression expression, IntegrationFlow subFlow) {
 		MessageChannel channel = obtainInputChannelFromFlow(subFlow);
 		return recipient(channel, expression);
 	}
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/RouterSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/RouterSpec.java
index 302150019f..5d0a93e016 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/RouterSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/RouterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,8 +42,7 @@ import org.springframework.util.StringUtils;
  *
  * @since 5.0
  */
-public final class RouterSpec<K, R extends AbstractMappingMessageRouter>
-		extends AbstractRouterSpec<RouterSpec<K, R>, R> {
+public class RouterSpec<K, R extends AbstractMappingMessageRouter> extends AbstractRouterSpec<RouterSpec<K, R>, R> {
 
 	private final RouterMappingProvider mappingProvider;
 
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/SourcePollingChannelAdapterSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/SourcePollingChannelAdapterSpec.java
index 47cb2b4ac8..594cf4641f 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/SourcePollingChannelAdapterSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/SourcePollingChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ package org.springframework.integration.dsl;
 import org.springframework.integration.config.SourcePollingChannelAdapterFactoryBean;
 import org.springframework.integration.core.MessageSource;
 import org.springframework.integration.scheduling.PollerMetadata;
+import org.springframework.lang.Nullable;
 
 /**
  * @author Artem Bilan
@@ -43,7 +44,7 @@ public class SourcePollingChannelAdapterSpec extends
 		return _this();
 	}
 
-	public SourcePollingChannelAdapterSpec poller(PollerMetadata pollerMetadata) {
+	public SourcePollingChannelAdapterSpec poller(@Nullable PollerMetadata pollerMetadata) {
 		if (pollerMetadata != null) {
 			if (PollerMetadata.MAX_MESSAGES_UNBOUNDED == pollerMetadata.getMaxMessagesPerPoll()) {
 				pollerMetadata.setMaxMessagesPerPoll(1);
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/StandardIntegrationFlow.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/StandardIntegrationFlow.java
index 7b1fdb69fe..c99bd4831d 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/StandardIntegrationFlow.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/StandardIntegrationFlow.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import java.util.concurrent.atomic.AtomicInteger;
 import org.springframework.beans.factory.BeanNameAware;
 import org.springframework.context.SmartLifecycle;
 import org.springframework.integration.support.context.NamedComponent;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 
 /**
@@ -102,6 +103,7 @@ public class StandardIntegrationFlow
 		throw new UnsupportedOperationException();
 	}
 
+	@Nullable
 	@Override
 	public MessageChannel getInputChannel() {
 		if (this.inputChannel == null) {
@@ -146,8 +148,7 @@ public class StandardIntegrationFlow
 	public void stop(Runnable callback) {
 		AggregatingCallback aggregatingCallback = new AggregatingCallback(this.integrationComponents.size(), callback);
 		for (Object component : this.integrationComponents.keySet()) {
-			if (component instanceof SmartLifecycle) {
-				SmartLifecycle lifecycle = (SmartLifecycle) component;
+			if (component instanceof SmartLifecycle lifecycle) {
 				if (lifecycle.isRunning()) {
 					lifecycle.stop(aggregatingCallback);
 					continue;
@@ -161,8 +162,7 @@ public class StandardIntegrationFlow
 	@Override
 	public void stop() {
 		for (Object component : this.integrationComponents.keySet()) {
-			if (component instanceof SmartLifecycle) {
-				SmartLifecycle lifecycle = (SmartLifecycle) component;
+			if (component instanceof SmartLifecycle lifecycle) {
 				if (lifecycle.isRunning()) {
 					lifecycle.stop();
 				}
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/WireTapSpec.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/WireTapSpec.java
index 882497063e..51cb0d6287 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/WireTapSpec.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/WireTapSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -104,7 +104,7 @@ public class WireTapSpec extends IntegrationComponentSpec<WireTapSpec, WireTap>
 			return Collections.singletonMap(this.selector, null);
 		}
 		else {
-			return null;
+			return Collections.emptyMap();
 		}
 	}
 
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowBeanPostProcessor.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowBeanPostProcessor.java
index f180061be4..cf91e734f4 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowBeanPostProcessor.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowBeanPostProcessor.java
@@ -72,6 +72,7 @@ import org.springframework.integration.dsl.StandardIntegrationFlow;
 import org.springframework.integration.dsl.support.MessageChannelReference;
 import org.springframework.integration.gateway.AnnotationGatewayProxyFactoryBean;
 import org.springframework.integration.support.context.NamedComponent;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageHandler;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
@@ -178,7 +179,7 @@ public class IntegrationFlowBeanPostProcessor
 				targetIntegrationComponents.put(endpoint, id);
 			}
 			else if (component instanceof MessageChannelReference messageChannelReference) {
-				String channelBeanName = messageChannelReference.getName();
+				String channelBeanName = messageChannelReference.name();
 				if (!this.beanFactory.containsBean(channelBeanName)) {
 					DirectChannel directChannel = new DirectChannel();
 					registerComponent(directChannel, channelBeanName, flowBeanName);
@@ -422,8 +423,7 @@ public class IntegrationFlowBeanPostProcessor
 		}
 
 		return !this.beanFactory.getBeansOfType(instance.getClass(), false, false)
-				.values()
-				.contains(instance);
+				.containsValue(instance);
 	}
 
 	private void registerComponent(Object component, String beanName) {
@@ -431,7 +431,7 @@ public class IntegrationFlowBeanPostProcessor
 	}
 
 	@SuppressWarnings("unchecked")
-	private void registerComponent(Object component, String beanName, String parentName,
+	private void registerComponent(Object component, String beanName, @Nullable String parentName,
 			BeanDefinitionCustomizer... customizers) {
 
 		AbstractBeanDefinition beanDefinition =
@@ -461,7 +461,9 @@ public class IntegrationFlowBeanPostProcessor
 		return generateBeanName(instance, prefix, null, false);
 	}
 
-	private String generateBeanName(Object instance, String prefix, String fallbackId, boolean useFlowIdAsPrefix) {
+	private String generateBeanName(Object instance, String prefix, @Nullable String fallbackId,
+			boolean useFlowIdAsPrefix) {
+
 		if (instance instanceof NamedComponent namedComponent && namedComponent.getBeanName() != null) {
 			String beanName = namedComponent.getBeanName();
 			return useFlowIdAsPrefix
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowContext.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowContext.java
index 9224e53b4a..31ad6c3b12 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowContext.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowContext.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2021 the original author or authors.
+ * Copyright 2018-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import java.util.Map;
 import org.springframework.beans.factory.BeanFactoryAware;
 import org.springframework.integration.core.MessagingTemplate;
 import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 
 /**
@@ -200,7 +201,7 @@ public interface IntegrationFlowContext {
 		 * @param bean an additional arbitrary bean to register into the application context.
 		 * @return the current builder instance
 		 */
-		IntegrationFlowRegistrationBuilder addBean(String name, Object bean);
+		IntegrationFlowRegistrationBuilder addBean(@Nullable String name, Object bean);
 
 		/**
 		 * Set the configuration source {@code Object} for this manual Integration flow definition.
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowLifecycleAdvice.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowLifecycleAdvice.java
index e98fe8dec0..d66d8d3be1 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowLifecycleAdvice.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/IntegrationFlowLifecycleAdvice.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2021 the original author or authors.
+ * Copyright 2018-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,11 +16,15 @@
 
 package org.springframework.integration.dsl.context;
 
+import java.util.Map;
+
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
 
 import org.springframework.context.SmartLifecycle;
 import org.springframework.integration.dsl.StandardIntegrationFlow;
+import org.springframework.lang.Nullable;
+import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -77,7 +81,7 @@ class IntegrationFlowLifecycleAdvice implements MethodInterceptor {
 		}
 		else if ("getIntegrationComponents".equals(method)) {
 			result = invocation.proceed();
-			if (result == null) {
+			if (CollectionUtils.isEmpty((Map<?, ?>) result)) {
 				result = this.delegate.getIntegrationComponents();
 			}
 		}
@@ -91,7 +95,8 @@ class IntegrationFlowLifecycleAdvice implements MethodInterceptor {
 		return result;
 	}
 
-	private Object applyToDelegate(MethodInvocation invocation, String method, Object resultArg) {
+	@Nullable
+	private Object applyToDelegate(MethodInvocation invocation, String method, @Nullable Object resultArg) {
 		Object result = resultArg;
 		switch (method) {
 
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/StandardIntegrationFlowContext.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/StandardIntegrationFlowContext.java
index c760735f11..be0ffc5748 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/StandardIntegrationFlowContext.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/StandardIntegrationFlowContext.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -242,7 +242,7 @@ public final class StandardIntegrationFlowContext implements IntegrationFlowCont
 		return Collections.unmodifiableMap(this.registry);
 	}
 
-	private String generateBeanName(Object instance, String parentName) {
+	private String generateBeanName(Object instance, @Nullable String parentName) {
 		if (instance instanceof NamedComponent) {
 			String beanName = ((NamedComponent) instance).getBeanName();
 			if (beanName != null) {
@@ -331,7 +331,7 @@ public final class StandardIntegrationFlowContext implements IntegrationFlowCont
 		 * @return the current builder instance
 		 */
 		@Override
-		public StandardIntegrationFlowRegistrationBuilder addBean(String name, Object bean) {
+		public StandardIntegrationFlowRegistrationBuilder addBean(@Nullable String name, Object bean) {
 			this.additionalBeans.put(bean, name);
 			return this;
 		}
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/package-info.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/package-info.java
index 22ecaef0c3..6067b368bf 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/package-info.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/context/package-info.java
@@ -1,4 +1,5 @@
 /**
  * The context support classes for Spring Integration Java DSL.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.integration.dsl.context;
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/package-info.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/package-info.java
index bcf137dab3..6d9ccd8569 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/package-info.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/package-info.java
@@ -1,4 +1,5 @@
 /**
  * Root package of the Spring Integration Java DSL.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.integration.dsl;
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/FixedSubscriberChannelPrototype.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/FixedSubscriberChannelPrototype.java
index a58f8a8e90..1206d8da3b 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/FixedSubscriberChannelPrototype.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/FixedSubscriberChannelPrototype.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.integration.dsl.support;
 
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
 
@@ -38,7 +39,7 @@ public class FixedSubscriberChannelPrototype implements MessageChannel {
 		this(null);
 	}
 
-	public FixedSubscriberChannelPrototype(String name) {
+	public FixedSubscriberChannelPrototype(@Nullable String name) {
 		this.name = name;
 	}
 
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/MessageChannelReference.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/MessageChannelReference.java
index e705fba0ab..02c3cef45a 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/MessageChannelReference.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/MessageChannelReference.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,24 +25,20 @@ import org.springframework.util.Assert;
  * {@link MessageChannel} bean on the bean registration phase.
  * For internal use only.
  *
+ * @param name the name of the target {@link MessageChannel} bean.
+ *
  * @author Artem Bilan
  *
  * @since 5.0
  *
  * @see org.springframework.integration.dsl.context.IntegrationFlowBeanPostProcessor
  */
-public class MessageChannelReference implements MessageChannel {
+public record MessageChannelReference(String name) implements MessageChannel {
 
-	private final String name;
-
-	public MessageChannelReference(String name) {
+	public MessageChannelReference {
 		Assert.notNull(name, "'name' must not be null");
-		this.name = name;
 	}
 
-	public String getName() {
-		return this.name;
-	}
 
 	@Override
 	public boolean send(Message<?> message) {
diff --git a/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/package-info.java b/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/package-info.java
index 1affe13084..16ab723fd2 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/package-info.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/dsl/support/package-info.java
@@ -1,4 +1,5 @@
 /**
  * Provides various support classes used across Spring Integration Java DSL Components.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.integration.dsl.support;
diff --git a/spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinIntegrationFlowDefinition.kt b/spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinIntegrationFlowDefinition.kt
index 517f837c9c..53568f4ff6 100644
--- a/spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinIntegrationFlowDefinition.kt
+++ b/spring-integration-core/src/main/kotlin/org/springframework/integration/dsl/KotlinIntegrationFlowDefinition.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2022 the original author or authors.
+ * Copyright 2020-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -901,6 +901,15 @@ class KotlinIntegrationFlowDefinition(@PublishedApi internal val delegate: Integ
 		this.delegate.gateway(requestChannel, Consumer(endpointConfigurer))
 	}
 
+	/**
+	 * Populate the "artificial"
+	 * [org.springframework.integration.gateway.GatewayMessageHandler] for the
+	 * provided `subflow` with options from [GatewayEndpointSpec].
+	 */
+	fun gateway(flow: IntegrationFlow) {
+		this.delegate.gateway(flow)
+	}
+
 	/**
 	 * Populate the "artificial"
 	 * [org.springframework.integration.gateway.GatewayMessageHandler] for the
diff --git a/spring-integration-core/src/test/java/org/springframework/integration/dsl/flowservices/FlowServiceTests.java b/spring-integration-core/src/test/java/org/springframework/integration/dsl/flowservices/FlowServiceTests.java
index e9495c2f2f..0150d87b2d 100644
--- a/spring-integration-core/src/test/java/org/springframework/integration/dsl/flowservices/FlowServiceTests.java
+++ b/spring-integration-core/src/test/java/org/springframework/integration/dsl/flowservices/FlowServiceTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicReference;
 
+import org.jetbrains.annotations.NotNull;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.aop.framework.Advised;
@@ -176,7 +177,7 @@ public class FlowServiceTests {
 		private final AtomicReference<Object> resultOverLoggingHandler = new AtomicReference<>();
 
 		@Override
-		public void configure(IntegrationFlowDefinition<?> f) {
+		public void configure(@NotNull IntegrationFlowDefinition<?> f) {
 			f.<String, String>transform(String::toUpperCase)
 					.log(LoggingHandler.Level.ERROR, m -> {
 						resultOverLoggingHandler.set(m.getPayload());
diff --git a/spring-integration-core/src/test/kotlin/org/springframework/integration/dsl/routers/RouterDslTests.kt b/spring-integration-core/src/test/kotlin/org/springframework/integration/dsl/routers/RouterDslTests.kt
index 9dcc9f7685..7a1b6d1716 100644
--- a/spring-integration-core/src/test/kotlin/org/springframework/integration/dsl/routers/RouterDslTests.kt
+++ b/spring-integration-core/src/test/kotlin/org/springframework/integration/dsl/routers/RouterDslTests.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2020 the original author or authors.
+ * Copyright 2018-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -114,8 +114,8 @@ class RouterDslTests {
 				integrationFlow {
 					split()
 					route<Int, Boolean>({ it % 2 == 0 }) {
-						subFlowMapping(true) { gateway(oddFlow().inputChannel) }
-						subFlowMapping(false) { gateway(evenFlow().inputChannel) }
+						subFlowMapping(true) { gateway(oddFlow()) }
+						subFlowMapping(false) { gateway(evenFlow()) }
 					}
 					aggregate()
 				}
diff --git a/spring-integration-feed/src/main/java/org/springframework/integration/feed/dsl/package-info.java b/spring-integration-feed/src/main/java/org/springframework/integration/feed/dsl/package-info.java
index 6b922a4896..b2f9816eda 100644
--- a/spring-integration-feed/src/main/java/org/springframework/integration/feed/dsl/package-info.java
+++ b/spring-integration-feed/src/main/java/org/springframework/integration/feed/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides Feed Components support for Spring Integration Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.feed.dsl;
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/config/FileTailInboundChannelAdapterFactoryBean.java b/spring-integration-file/src/main/java/org/springframework/integration/file/config/FileTailInboundChannelAdapterFactoryBean.java
index 683011f905..35c86db47e 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/config/FileTailInboundChannelAdapterFactoryBean.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/config/FileTailInboundChannelAdapterFactoryBean.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import org.springframework.integration.JavaUtils;
 import org.springframework.integration.file.tail.ApacheCommonsFileTailingMessageProducer;
 import org.springframework.integration.file.tail.FileTailingMessageProducerSupport;
 import org.springframework.integration.file.tail.OSDelegatingFileTailingMessageProducer;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.scheduling.TaskScheduler;
 import org.springframework.util.Assert;
@@ -137,7 +138,7 @@ public class FileTailInboundChannelAdapterFactoryBean extends AbstractFactoryBea
 	}
 
 	@Override
-	public void setBeanName(String name) {
+	public void setBeanName(@Nullable String name) {
 		this.beanName = name;
 	}
 
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileInboundChannelAdapterSpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileInboundChannelAdapterSpec.java
index 342297a30f..1d8de28007 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileInboundChannelAdapterSpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileInboundChannelAdapterSpec.java
@@ -36,6 +36,7 @@ import org.springframework.integration.file.config.FileListFilterFactoryBean;
 import org.springframework.integration.file.filters.ExpressionFileListFilter;
 import org.springframework.integration.file.filters.FileListFilter;
 import org.springframework.integration.file.locking.NioFileLocker;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -51,10 +52,13 @@ public class FileInboundChannelAdapterSpec
 
 	protected final FileListFilterFactoryBean fileListFilterFactoryBean = new FileListFilterFactoryBean(); // NOSONAR
 
+	@Nullable
 	private FileLocker locker;
 
+	@Nullable
 	private ExpressionFileListFilter<File> expressionFileListFilter;
 
+	@Nullable
 	private DirectoryScanner scanner;
 
 	private boolean filtersSet;
@@ -63,7 +67,7 @@ public class FileInboundChannelAdapterSpec
 		this.target = new FileReadingMessageSource();
 	}
 
-	protected FileInboundChannelAdapterSpec(Comparator<File> receptionOrderComparator) {
+	protected FileInboundChannelAdapterSpec(@Nullable Comparator<File> receptionOrderComparator) {
 		this.target = new FileReadingMessageSource(receptionOrderComparator);
 	}
 
@@ -314,7 +318,7 @@ public class FileInboundChannelAdapterSpec
 			return Collections.singletonMap(this.expressionFileListFilter, null);
 		}
 		else {
-			return null;
+			return Collections.emptyMap();
 		}
 	}
 
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileSplitterSpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileSplitterSpec.java
index a7435772c2..4cec1d3d8d 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileSplitterSpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileSplitterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.nio.charset.Charset;
 
 import org.springframework.integration.dsl.MessageHandlerSpec;
 import org.springframework.integration.file.splitter.FileSplitter;
+import org.springframework.lang.Nullable;
 import org.springframework.util.StringUtils;
 
 /**
@@ -39,10 +40,12 @@ public class FileSplitterSpec extends MessageHandlerSpec<FileSplitterSpec, FileS
 
 	private boolean markersJson;
 
+	@Nullable
 	private Charset charset;
 
 	private boolean applySequence;
 
+	@Nullable
 	private String firstLineHeaderName;
 
 	protected FileSplitterSpec() {
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileTransferringMessageHandlerSpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileTransferringMessageHandlerSpec.java
index 4e58423fb8..4a12209cb2 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileTransferringMessageHandlerSpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileTransferringMessageHandlerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,7 @@ import org.springframework.integration.file.remote.RemoteFileTemplate;
 import org.springframework.integration.file.remote.handler.FileTransferringMessageHandler;
 import org.springframework.integration.file.remote.session.SessionFactory;
 import org.springframework.integration.file.support.FileExistsMode;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 
@@ -49,8 +50,10 @@ public abstract class FileTransferringMessageHandlerSpec<F, S extends FileTransf
 		extends MessageHandlerSpec<S, FileTransferringMessageHandler<F>>
 		implements ComponentsRegistration {
 
+	@Nullable
 	private FileNameGenerator fileNameGenerator;
 
+	@Nullable
 	private DefaultFileNameGenerator defaultFileNameGenerator;
 
 	// TODO: should be refactored using generics in next release (breaking change), see PR-3080.
@@ -238,7 +241,7 @@ public abstract class FileTransferringMessageHandlerSpec<F, S extends FileTransf
 		if (this.defaultFileNameGenerator != null) {
 			return Collections.singletonMap(this.defaultFileNameGenerator, null);
 		}
-		return null;
+		return Collections.emptyMap();
 	}
 
 }
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileWritingMessageHandlerSpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileWritingMessageHandlerSpec.java
index a7fba0dca3..5db40aeed5 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileWritingMessageHandlerSpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/FileWritingMessageHandlerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import org.springframework.integration.file.DefaultFileNameGenerator;
 import org.springframework.integration.file.FileNameGenerator;
 import org.springframework.integration.file.FileWritingMessageHandler;
 import org.springframework.integration.file.support.FileExistsMode;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.scheduling.TaskScheduler;
 import org.springframework.util.Assert;
@@ -45,8 +46,10 @@ public class FileWritingMessageHandlerSpec
 		extends MessageHandlerSpec<FileWritingMessageHandlerSpec, FileWritingMessageHandler>
 		implements ComponentsRegistration {
 
+	@Nullable
 	private FileNameGenerator fileNameGenerator;
 
+	@Nullable
 	private DefaultFileNameGenerator defaultFileNameGenerator;
 
 	protected FileWritingMessageHandlerSpec(File destinationDirectory) {
@@ -264,7 +267,7 @@ public class FileWritingMessageHandlerSpec
 		if (this.defaultFileNameGenerator != null) {
 			return Collections.singletonMap(this.defaultFileNameGenerator, null);
 		}
-		return null;
+		return Collections.emptyMap();
 	}
 
 }
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/Files.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/Files.java
index cb4d7f2db4..c934d21c83 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/Files.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/Files.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import java.util.function.Function;
 import org.springframework.expression.Expression;
 import org.springframework.integration.file.transformer.FileToByteArrayTransformer;
 import org.springframework.integration.file.transformer.FileToStringTransformer;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 
 /**
@@ -50,7 +51,8 @@ public abstract class Files {
 	 * @return the {@link FileInboundChannelAdapterSpec} instance.
 	 */
 	public static FileInboundChannelAdapterSpec inboundAdapter(File directory,
-			Comparator<File> receptionOrderComparator) {
+			@Nullable Comparator<File> receptionOrderComparator) {
+
 		return new FileInboundChannelAdapterSpec(receptionOrderComparator).directory(directory);
 	}
 
@@ -197,7 +199,7 @@ public abstract class Files {
 	 * @param deleteFiles true to delete the file.
 	 * @return the {@link FileToStringTransformer}.
 	 */
-	public static FileToStringTransformer toStringTransformer(String charset, boolean deleteFiles) {
+	public static FileToStringTransformer toStringTransformer(@Nullable String charset, boolean deleteFiles) {
 		FileToStringTransformer transformer = new FileToStringTransformer();
 		if (charset != null) {
 			transformer.setCharset(charset);
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileInboundChannelAdapterSpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileInboundChannelAdapterSpec.java
index 1454660f88..5cf4c6fdbe 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileInboundChannelAdapterSpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,6 +32,7 @@ import org.springframework.integration.file.filters.FileListFilter;
 import org.springframework.integration.file.remote.synchronizer.AbstractInboundFileSynchronizer;
 import org.springframework.integration.file.remote.synchronizer.AbstractInboundFileSynchronizingMessageSource;
 import org.springframework.integration.metadata.MetadataStore;
+import org.springframework.lang.Nullable;
 
 /**
  * A {@link MessageSourceSpec} for an {@link AbstractInboundFileSynchronizingMessageSource}.
@@ -52,6 +53,7 @@ public abstract class RemoteFileInboundChannelAdapterSpec<F, S extends RemoteFil
 
 	protected final AbstractInboundFileSynchronizer<F> synchronizer; // NOSONAR final
 
+	@Nullable
 	private ExpressionFileListFilter<F> expressionFileListFilter;
 
 	protected RemoteFileInboundChannelAdapterSpec(AbstractInboundFileSynchronizer<F> synchronizer) {
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileOutboundGatewaySpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileOutboundGatewaySpec.java
index 63b769879f..a566aea78a 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileOutboundGatewaySpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileOutboundGatewaySpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,6 +33,7 @@ import org.springframework.integration.file.filters.RegexPatternFileListFilter;
 import org.springframework.integration.file.filters.SimplePatternFileListFilter;
 import org.springframework.integration.file.remote.gateway.AbstractRemoteFileOutboundGateway;
 import org.springframework.integration.file.support.FileExistsMode;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 
 /**
@@ -50,12 +51,16 @@ public abstract class RemoteFileOutboundGatewaySpec<F, S extends RemoteFileOutbo
 		extends MessageHandlerSpec<S, AbstractRemoteFileOutboundGateway<F>>
 		implements ComponentsRegistration {
 
+	@Nullable
 	private CompositeFileListFilter<F> filter;
 
+	@Nullable
 	private ExpressionFileListFilter<F> expressionFileListFilter;
 
+	@Nullable
 	private ExpressionFileListFilter<File> mputExpressionFileListFilter;
 
+	@Nullable
 	private CompositeFileListFilter<File> mputFilter;
 
 	protected RemoteFileOutboundGatewaySpec(AbstractRemoteFileOutboundGateway<F> outboundGateway) {
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileStreamingInboundChannelAdapterSpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileStreamingInboundChannelAdapterSpec.java
index 2befbf7d39..94f09c89e5 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileStreamingInboundChannelAdapterSpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/RemoteFileStreamingInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import org.springframework.integration.expression.FunctionExpression;
 import org.springframework.integration.file.filters.ExpressionFileListFilter;
 import org.springframework.integration.file.filters.FileListFilter;
 import org.springframework.integration.file.remote.AbstractRemoteFileStreamingMessageSource;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 
 /**
@@ -46,6 +47,7 @@ public abstract class RemoteFileStreamingInboundChannelAdapterSpec<F,
 		extends MessageSourceSpec<S, MS>
 		implements ComponentsRegistration {
 
+	@Nullable
 	private ExpressionFileListFilter<F> expressionFileListFilter;
 
 	/**
@@ -143,7 +145,7 @@ public abstract class RemoteFileStreamingInboundChannelAdapterSpec<F,
 			return Collections.singletonMap(this.expressionFileListFilter, null);
 		}
 		else {
-			return null;
+			return Collections.emptyMap();
 		}
 	}
 
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/TailAdapterSpec.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/TailAdapterSpec.java
index 1ee53e1c72..17c03d141c 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/TailAdapterSpec.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/TailAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import org.springframework.core.task.TaskExecutor;
 import org.springframework.integration.dsl.MessageProducerSpec;
 import org.springframework.integration.file.config.FileTailInboundChannelAdapterFactoryBean;
 import org.springframework.integration.file.tail.FileTailingMessageProducerSupport;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.scheduling.TaskScheduler;
 import org.springframework.util.Assert;
@@ -39,8 +40,10 @@ public class TailAdapterSpec extends MessageProducerSpec<TailAdapterSpec, FileTa
 
 	private final FileTailInboundChannelAdapterFactoryBean factoryBean = new FileTailInboundChannelAdapterFactoryBean();
 
+	@Nullable
 	private MessageChannel outputChannel;
 
+	@Nullable
 	private MessageChannel errorChannel;
 
 	protected TailAdapterSpec() {
@@ -155,7 +158,7 @@ public class TailAdapterSpec extends MessageProducerSpec<TailAdapterSpec, FileTa
 	}
 
 	@Override
-	public TailAdapterSpec id(String id) {
+	public TailAdapterSpec id(@Nullable String id) {
 		this.factoryBean.setBeanName(id);
 		return _this();
 	}
@@ -186,14 +189,16 @@ public class TailAdapterSpec extends MessageProducerSpec<TailAdapterSpec, FileTa
 
 	@Override
 	protected FileTailingMessageProducerSupport doGet() {
-		FileTailingMessageProducerSupport tailingMessageProducerSupport = null;
+		FileTailingMessageProducerSupport tailingMessageProducerSupport;
 		try {
 			this.factoryBean.afterPropertiesSet();
 			tailingMessageProducerSupport = this.factoryBean.getObject();
 		}
-		catch (Exception e) {
-			throw new IllegalStateException(e);
+		catch (Exception ex) {
+			throw new IllegalStateException(ex);
 		}
+		Assert.notNull(tailingMessageProducerSupport,
+				"The 'FileTailInboundChannelAdapterFactoryBean' must not produce null");
 		if (this.errorChannel != null) {
 			tailingMessageProducerSupport.setErrorChannel(this.errorChannel);
 		}
diff --git a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/package-info.java b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/package-info.java
index 4a447e5f7c..8c4996a759 100644
--- a/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/package-info.java
+++ b/spring-integration-file/src/main/java/org/springframework/integration/file/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides File Components support for Spring Integration Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.file.dsl;
diff --git a/spring-integration-file/src/test/kotlin/org/springframework/integration/kotlin/file/aggregator/KotlinFileAggregatorTests.kt b/spring-integration-file/src/test/kotlin/org/springframework/integration/kotlin/file/aggregator/KotlinFileAggregatorTests.kt
index cd660ec518..443df3fe44 100644
--- a/spring-integration-file/src/test/kotlin/org/springframework/integration/kotlin/file/aggregator/KotlinFileAggregatorTests.kt
+++ b/spring-integration-file/src/test/kotlin/org/springframework/integration/kotlin/file/aggregator/KotlinFileAggregatorTests.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2021-2022 the original author or authors.
+ * Copyright 2021-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -102,7 +102,7 @@ class KotlinFileAggregatorTests {
 	class Config {
 
 		@Bean
-		fun fileSplitterAggregatorFlow(taskExecutor: TaskExecutor?) =
+		fun fileSplitterAggregatorFlow(taskExecutor: TaskExecutor) =
 			integrationFlow {
 				split(Files.splitter().markers().firstLineAsHeader("firstLine"))
 				channel { executor(taskExecutor) }
@@ -115,4 +115,4 @@ class KotlinFileAggregatorTests {
 
 	}
 
-}
\ No newline at end of file
+}
diff --git a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/Ftp.java b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/Ftp.java
index 0226b2160d..de64a2b408 100644
--- a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/Ftp.java
+++ b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/Ftp.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2022 the original author or authors.
+ * Copyright 2014-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@ import org.springframework.integration.file.remote.session.SessionFactory;
 import org.springframework.integration.file.support.FileExistsMode;
 import org.springframework.integration.ftp.gateway.FtpOutboundGateway;
 import org.springframework.integration.ftp.session.FtpRemoteFileTemplate;
+import org.springframework.lang.Nullable;
 
 /**
  * The factory for FTP components.
@@ -56,7 +57,7 @@ public final class Ftp {
 	 * @return the spec.
 	 */
 	public static FtpInboundChannelAdapterSpec inboundAdapter(SessionFactory<FTPFile> sessionFactory,
-			Comparator<File> receptionOrderComparator) {
+			@Nullable Comparator<File> receptionOrderComparator) {
 
 		return new FtpInboundChannelAdapterSpec(sessionFactory, receptionOrderComparator);
 	}
@@ -82,7 +83,7 @@ public final class Ftp {
 	 */
 	public static FtpStreamingInboundChannelAdapterSpec inboundStreamingAdapter(
 			RemoteFileTemplate<FTPFile> remoteFileTemplate,
-			Comparator<FTPFile> receptionOrderComparator) {
+			@Nullable Comparator<FTPFile> receptionOrderComparator) {
 
 		return new FtpStreamingInboundChannelAdapterSpec(remoteFileTemplate, receptionOrderComparator);
 	}
diff --git a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpInboundChannelAdapterSpec.java b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpInboundChannelAdapterSpec.java
index 19fca2f466..3fb88c2c2f 100644
--- a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpInboundChannelAdapterSpec.java
+++ b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2022 the original author or authors.
+ * Copyright 2014-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,7 @@ import org.springframework.integration.ftp.filters.FtpSimplePatternFileListFilte
 import org.springframework.integration.ftp.inbound.FtpInboundFileSynchronizer;
 import org.springframework.integration.ftp.inbound.FtpInboundFileSynchronizingMessageSource;
 import org.springframework.integration.metadata.SimpleMetadataStore;
+import org.springframework.lang.Nullable;
 
 /**
  * A {@link RemoteFileInboundChannelAdapterSpec} for an {@link FtpInboundFileSynchronizingMessageSource}.
@@ -43,7 +44,9 @@ public class FtpInboundChannelAdapterSpec
 		extends RemoteFileInboundChannelAdapterSpec<FTPFile, FtpInboundChannelAdapterSpec,
 		FtpInboundFileSynchronizingMessageSource> {
 
-	protected FtpInboundChannelAdapterSpec(SessionFactory<FTPFile> sessionFactory, Comparator<File> comparator) {
+	protected FtpInboundChannelAdapterSpec(SessionFactory<FTPFile> sessionFactory,
+			@Nullable Comparator<File> comparator) {
+
 		super(new FtpInboundFileSynchronizer(sessionFactory));
 		this.target = new FtpInboundFileSynchronizingMessageSource(this.synchronizer, comparator);
 	}
diff --git a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpStreamingInboundChannelAdapterSpec.java b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpStreamingInboundChannelAdapterSpec.java
index 5d77f39082..14b0e00ae1 100644
--- a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpStreamingInboundChannelAdapterSpec.java
+++ b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/FtpStreamingInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2022 the original author or authors.
+ * Copyright 2014-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import org.springframework.integration.ftp.filters.FtpRegexPatternFileListFilter
 import org.springframework.integration.ftp.filters.FtpSimplePatternFileListFilter;
 import org.springframework.integration.ftp.inbound.FtpStreamingMessageSource;
 import org.springframework.integration.metadata.SimpleMetadataStore;
+import org.springframework.lang.Nullable;
 
 /**
  * A {@link RemoteFileStreamingInboundChannelAdapterSpec} for a {@link FtpStreamingMessageSource}.
@@ -43,7 +44,7 @@ public class FtpStreamingInboundChannelAdapterSpec
 		FtpStreamingMessageSource> {
 
 	protected FtpStreamingInboundChannelAdapterSpec(RemoteFileTemplate<FTPFile> remoteFileTemplate,
-			Comparator<FTPFile> comparator) {
+			@Nullable Comparator<FTPFile> comparator) {
 
 		this.target = new FtpStreamingMessageSource(remoteFileTemplate, comparator);
 	}
diff --git a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/package-info.java b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/package-info.java
index c5c25396db..55e82bb003 100644
--- a/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/package-info.java
+++ b/spring-integration-ftp/src/main/java/org/springframework/integration/ftp/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides FTP Components for the Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.ftp.dsl;
diff --git a/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/dsl/package-info.java b/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/dsl/package-info.java
index d06699f4c4..3930ab8ee1 100644
--- a/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/dsl/package-info.java
+++ b/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides classes for Java DSL to support GraphQL components.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.graphql.dsl;
diff --git a/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/GraphQlMessageHandler.java b/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/GraphQlMessageHandler.java
index 05b1fc5d2e..58edacdf8d 100644
--- a/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/GraphQlMessageHandler.java
+++ b/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/GraphQlMessageHandler.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -47,8 +47,9 @@ public class GraphQlMessageHandler extends AbstractReplyProducingMessageHandler
 
 	private final ExecutionGraphQlService graphQlService;
 
-	private StandardEvaluationContext evaluationContext;
+	private StandardEvaluationContext evaluationContext = new StandardEvaluationContext();
 
+	@Nullable
 	private Expression operationExpression;
 
 	private Expression operationNameExpression = new SupplierExpression<>(() -> null);
@@ -142,11 +143,11 @@ public class GraphQlMessageHandler extends AbstractReplyProducingMessageHandler
 			graphQlRequest = (ExecutionGraphQlRequest) requestMessage.getPayload();
 		}
 		else {
-			Assert.notNull(this.operationExpression, "'operationExpression' must not be null");
 			String query = evaluateOperationExpression(requestMessage);
 			String operationName = evaluateOperationNameExpression(requestMessage);
 			Map<String, Object> variables = evaluateVariablesExpression(requestMessage);
 			String id = evaluateExecutionIdExpression(requestMessage);
+			Assert.notNull(id, "The 'executionIdExpression' must not evaluate to null");
 			graphQlRequest = new DefaultExecutionGraphQlRequest(query, operationName, variables, null, id, this.locale);
 		}
 
@@ -155,20 +156,24 @@ public class GraphQlMessageHandler extends AbstractReplyProducingMessageHandler
 	}
 
 	private String evaluateOperationExpression(Message<?> message) {
+		Assert.notNull(this.operationExpression, "'operationExpression' must not be null");
 		String operation = this.operationExpression.getValue(this.evaluationContext, message, String.class);
 		Assert.notNull(operation, "'operationExpression' must not evaluate to null");
 		return operation;
 	}
 
+	@Nullable
 	private String evaluateOperationNameExpression(Message<?> message) {
 		return this.operationNameExpression.getValue(this.evaluationContext, message, String.class);
 	}
 
+	@Nullable
 	@SuppressWarnings("unchecked")
 	private Map<String, Object> evaluateVariablesExpression(Message<?> message) {
 		return this.variablesExpression.getValue(this.evaluationContext, message, Map.class);
 	}
 
+	@Nullable
 	private String evaluateExecutionIdExpression(Message<?> message) {
 		return this.executionIdExpression.getValue(this.evaluationContext, message, String.class);
 	}
diff --git a/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/package-info.java b/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/package-info.java
index 07a6db100a..da8bcdfddd 100644
--- a/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/package-info.java
+++ b/spring-integration-graphql/src/main/java/org/springframework/integration/graphql/outbound/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides classes for GraphQL outbound channel adapters.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.graphql.outbound;
diff --git a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/BaseHttpMessageHandlerSpec.java b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/BaseHttpMessageHandlerSpec.java
index 95962cdfa6..1050b9745c 100644
--- a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/BaseHttpMessageHandlerSpec.java
+++ b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/BaseHttpMessageHandlerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2021 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -112,7 +112,7 @@ public abstract class BaseHttpMessageHandlerSpec<S extends BaseHttpMessageHandle
 	/**
 	 * Specify whether the outbound message's payload should be extracted
 	 * when preparing the request body.
-	 * Otherwise the Message instance itself is serialized.
+	 * Otherwise, the Message instance itself is serialized.
 	 * The default value is {@code true}.
 	 * @param extractPayload true if the payload should be extracted.
 	 * @return the spec
@@ -174,6 +174,7 @@ public abstract class BaseHttpMessageHandlerSpec<S extends BaseHttpMessageHandle
 	 */
 	public <P> S expectedResponseTypeFunction(
 			Function<Message<P>, ?> expectedResponseTypeFunction) {
+
 		return expectedResponseTypeExpression(new FunctionExpression<>(expectedResponseTypeFunction));
 	}
 
diff --git a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/Http.java b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/Http.java
index 939839fbd9..00ae424fa5 100644
--- a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/Http.java
+++ b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/Http.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@ import org.springframework.expression.common.LiteralExpression;
 import org.springframework.integration.expression.FunctionExpression;
 import org.springframework.integration.http.inbound.HttpRequestHandlingController;
 import org.springframework.integration.http.inbound.HttpRequestHandlingMessagingGateway;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 import org.springframework.web.client.RestTemplate;
@@ -84,7 +85,7 @@ public final class Http {
 	 * @param restTemplate {@link RestTemplate} to use.
 	 * @return the HttpMessageHandlerSpec instance
 	 */
-	public static HttpMessageHandlerSpec outboundChannelAdapter(URI uri, RestTemplate restTemplate) {
+	public static HttpMessageHandlerSpec outboundChannelAdapter(URI uri, @Nullable RestTemplate restTemplate) {
 		return new HttpMessageHandlerSpec(uri, restTemplate).expectReply(false);
 	}
 
@@ -95,7 +96,7 @@ public final class Http {
 	 * @param restTemplate {@link RestTemplate} to use.
 	 * @return the HttpMessageHandlerSpec instance
 	 */
-	public static HttpMessageHandlerSpec outboundChannelAdapter(String uri, RestTemplate restTemplate) {
+	public static HttpMessageHandlerSpec outboundChannelAdapter(String uri, @Nullable RestTemplate restTemplate) {
 		return new HttpMessageHandlerSpec(uri, restTemplate).expectReply(false);
 	}
 
@@ -122,7 +123,9 @@ public final class Http {
 	 * @param restTemplate {@link RestTemplate} to use.
 	 * @return the HttpMessageHandlerSpec instance
 	 */
-	public static HttpMessageHandlerSpec outboundChannelAdapter(Expression uriExpression, RestTemplate restTemplate) {
+	public static HttpMessageHandlerSpec outboundChannelAdapter(Expression uriExpression,
+			@Nullable RestTemplate restTemplate) {
+
 		return new HttpMessageHandlerSpec(uriExpression, restTemplate).expectReply(false);
 	}
 
@@ -172,7 +175,7 @@ public final class Http {
 	 * @param restTemplate {@link RestTemplate} to use.
 	 * @return the HttpMessageHandlerSpec instance
 	 */
-	public static HttpMessageHandlerSpec outboundGateway(URI uri, RestTemplate restTemplate) {
+	public static HttpMessageHandlerSpec outboundGateway(URI uri, @Nullable RestTemplate restTemplate) {
 		return new HttpMessageHandlerSpec(uri, restTemplate);
 	}
 
@@ -183,7 +186,7 @@ public final class Http {
 	 * @param restTemplate {@link RestTemplate} to use.
 	 * @return the HttpMessageHandlerSpec instance
 	 */
-	public static HttpMessageHandlerSpec outboundGateway(String uri, RestTemplate restTemplate) {
+	public static HttpMessageHandlerSpec outboundGateway(String uri, @Nullable RestTemplate restTemplate) {
 		return new HttpMessageHandlerSpec(uri, restTemplate);
 	}
 
@@ -210,7 +213,9 @@ public final class Http {
 	 * @param restTemplate {@link RestTemplate} to use.
 	 * @return the HttpMessageHandlerSpec instance
 	 */
-	public static HttpMessageHandlerSpec outboundGateway(Expression uriExpression, RestTemplate restTemplate) {
+	public static HttpMessageHandlerSpec outboundGateway(Expression uriExpression,
+			@Nullable RestTemplate restTemplate) {
+
 		return new HttpMessageHandlerSpec(uriExpression, restTemplate);
 	}
 
diff --git a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpInboundEndpointSupportSpec.java b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpInboundEndpointSupportSpec.java
index 384d9df525..fc955e9ee0 100644
--- a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpInboundEndpointSupportSpec.java
+++ b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpInboundEndpointSupportSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2021 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -36,6 +36,7 @@ import org.springframework.integration.http.inbound.CrossOrigin;
 import org.springframework.integration.http.inbound.RequestMapping;
 import org.springframework.integration.http.support.DefaultHttpHeaderMapper;
 import org.springframework.integration.mapping.HeaderMapper;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.validation.Validator;
 import org.springframework.web.bind.annotation.RequestMethod;
@@ -60,6 +61,7 @@ public abstract class HttpInboundEndpointSupportSpec<S extends HttpInboundEndpoi
 
 	protected final HeaderMapper<HttpHeaders> headerMapper = DefaultHttpHeaderMapper.inboundMapper(); // NOSONAR final
 
+	@Nullable
 	private HeaderMapper<HttpHeaders> explicitHeaderMapper;
 
 	protected HttpInboundEndpointSupportSpec(E gateway, String... path) {
@@ -216,7 +218,7 @@ public abstract class HttpInboundEndpointSupportSpec<S extends HttpInboundEndpoi
 	/**
 	 * Specify the type of payload to be generated when the inbound HTTP request content is read by the
 	 * {@link org.springframework.http.converter.HttpMessageConverter}s.
-	 * By default this value is null which means at runtime any "text" Content-Type will
+	 * By default, this value is null which means at runtime any "text" Content-Type will
 	 * result in String while all others default to {@code byte[].class}.
 	 * @param requestPayloadType The payload type.
 	 * @return the current Spec.
@@ -229,7 +231,7 @@ public abstract class HttpInboundEndpointSupportSpec<S extends HttpInboundEndpoi
 	/**
 	 * Specify the type of payload to be generated when the inbound HTTP request content is read by the
 	 * {@link org.springframework.http.converter.HttpMessageConverter}s.
-	 * By default this value is null which means at runtime any "text" Content-Type will
+	 * By default, this value is null which means at runtime any "text" Content-Type will
 	 * result in String while all others default to {@code byte[].class}.
 	 * @param requestPayloadType The payload type.
 	 * @return the current Spec.
@@ -358,7 +360,7 @@ public abstract class HttpInboundEndpointSupportSpec<S extends HttpInboundEndpoi
 
 		/**
 		 * The producible media types of the mapped request, narrowing the primary mapping.
-		 * @param produces the the media types for {@code Accept} header.
+		 * @param produces the media types for {@code Accept} header.
 		 * @return the spec
 		 */
 		public RequestMappingSpec produces(String... produces) {
diff --git a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpMessageHandlerSpec.java b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpMessageHandlerSpec.java
index e0951deeba..ad1dc45c27 100644
--- a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpMessageHandlerSpec.java
+++ b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/HttpMessageHandlerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.integration.expression.ValueExpression;
 import org.springframework.integration.http.outbound.HttpRequestExecutingMessageHandler;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.web.client.ResponseErrorHandler;
 import org.springframework.web.client.RestTemplate;
@@ -43,17 +44,18 @@ import org.springframework.web.client.RestTemplate;
 public class HttpMessageHandlerSpec
 		extends BaseHttpMessageHandlerSpec<HttpMessageHandlerSpec, HttpRequestExecutingMessageHandler> {
 
+	@Nullable
 	private final RestTemplate restTemplate;
 
-	protected HttpMessageHandlerSpec(URI uri, RestTemplate restTemplate) {
+	protected HttpMessageHandlerSpec(URI uri, @Nullable RestTemplate restTemplate) {
 		this(new ValueExpression<>(uri), restTemplate);
 	}
 
-	protected HttpMessageHandlerSpec(String uri, RestTemplate restTemplate) {
+	protected HttpMessageHandlerSpec(String uri, @Nullable RestTemplate restTemplate) {
 		this(new LiteralExpression(uri), restTemplate);
 	}
 
-	protected HttpMessageHandlerSpec(Expression uriExpression, RestTemplate restTemplate) {
+	protected HttpMessageHandlerSpec(Expression uriExpression, @Nullable RestTemplate restTemplate) {
 		super(new HttpRequestExecutingMessageHandler(uriExpression, restTemplate));
 		this.restTemplate = restTemplate;
 	}
diff --git a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/package-info.java b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/package-info.java
index d650fcd421..f0bab4f1ed 100644
--- a/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/package-info.java
+++ b/spring-integration-http/src/main/java/org/springframework/integration/http/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides HTTP Components support for Spring Integration Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.http.dsl;
diff --git a/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/Jms.java b/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/Jms.java
index e3cba216ff..792d0adf8f 100644
--- a/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/Jms.java
+++ b/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/Jms.java
@@ -55,7 +55,9 @@ public final class Jms {
 	 */
 	public static JmsPollableMessageChannelSpec<?, PollableJmsChannel> pollableChannel(@Nullable String id,
 			ConnectionFactory connectionFactory) {
-		JmsPollableMessageChannelSpec<?, PollableJmsChannel> spec = new JmsPollableMessageChannelSpec<>(connectionFactory);
+
+		JmsPollableMessageChannelSpec<?, PollableJmsChannel> spec =
+				new JmsPollableMessageChannelSpec<>(connectionFactory);
 		return spec.id(id);
 	}
 
@@ -166,14 +168,9 @@ public final class Jms {
 	public static JmsInboundGatewaySpec.JmsInboundGatewayListenerContainerSpec<JmsDefaultListenerContainerSpec, DefaultMessageListenerContainer>
 	inboundGateway(ConnectionFactory connectionFactory) {
 
-		try {
-			return new JmsInboundGatewaySpec.JmsInboundGatewayListenerContainerSpec<>(
-					new JmsDefaultListenerContainerSpec()
-							.connectionFactory(connectionFactory));
-		}
-		catch (Exception e) {
-			throw new IllegalStateException(e);
-		}
+		return new JmsInboundGatewaySpec.JmsInboundGatewayListenerContainerSpec<>(
+				new JmsDefaultListenerContainerSpec()
+						.connectionFactory(connectionFactory));
 	}
 
 	/**
@@ -189,15 +186,10 @@ public final class Jms {
 	JmsInboundGatewaySpec.JmsInboundGatewayListenerContainerSpec<?, C> inboundGateway(
 			ConnectionFactory connectionFactory, Class<C> containerClass) {
 
-		try {
-			JmsListenerContainerSpec<?, C> spec =
-					new JmsListenerContainerSpec<>(containerClass)
-							.connectionFactory(connectionFactory);
-			return new JmsInboundGatewaySpec.JmsInboundGatewayListenerContainerSpec(spec);
-		}
-		catch (Exception e) {
-			throw new IllegalStateException(e);
-		}
+		JmsListenerContainerSpec<?, C> spec =
+				new JmsListenerContainerSpec<>(containerClass)
+						.connectionFactory(connectionFactory);
+		return new JmsInboundGatewaySpec.JmsInboundGatewayListenerContainerSpec(spec);
 	}
 
 	/**
diff --git a/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/JmsDestinationAccessorSpec.java b/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/JmsDestinationAccessorSpec.java
index d40296dc4d..6f4c96ab47 100644
--- a/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/JmsDestinationAccessorSpec.java
+++ b/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/JmsDestinationAccessorSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import jakarta.jms.ConnectionFactory;
 import org.springframework.integration.dsl.IntegrationComponentSpec;
 import org.springframework.jms.support.destination.DestinationResolver;
 import org.springframework.jms.support.destination.JmsDestinationAccessor;
+import org.springframework.lang.Nullable;
 
 /**
  * A base {@link IntegrationComponentSpec} for {@link JmsDestinationAccessor}s.
@@ -45,7 +46,7 @@ public abstract class JmsDestinationAccessorSpec<S extends JmsDestinationAccesso
 	}
 
 	@Override
-	public S id(String id) { // NOSONAR - not useless, increases visibility
+	public S id(@Nullable String id) { // NOSONAR - not useless, increases visibility
 		return super.id(id);
 	}
 
diff --git a/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/package-info.java b/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/package-info.java
index e3d6f8c571..3cce2af0de 100644
--- a/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/package-info.java
+++ b/spring-integration-jms/src/main/java/org/springframework/integration/jms/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides JMS Component support for the Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.jms.dsl;
diff --git a/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaInboundChannelAdapterSpec.java b/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaInboundChannelAdapterSpec.java
index de75c7b23c..e4760c9d36 100644
--- a/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaInboundChannelAdapterSpec.java
+++ b/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -98,10 +98,10 @@ public class JpaInboundChannelAdapterSpec
 
 	/**
 	 * If not set, this property defaults to <code>false</code>, which means that
-	 * deletion occurs on a per object basis if a collection of entities is being
+	 * deletion occurs on a per-object basis if a collection of entities is being
 	 * deleted.
 	 *<p>If set to 'true' the elements of the payload are deleted as a batch
-	 * operation. Be aware that this exhibits issues in regards to cascaded deletes.
+	 * operation. Be aware that this exhibits issues in regard to cascaded deletes.
 	 *<p>The specification 'JSR 317: Java Persistence API, Version 2.0' does not
 	 * support cascaded deletes in batch operations. The specification states in
 	 * chapter 4.10:
@@ -152,7 +152,7 @@ public class JpaInboundChannelAdapterSpec
 	}
 
 	/**
-	 * Set the maximum number of results expression. It has be a non null value
+	 * Set the maximum number of results expression. It has to be a non-null value
 	 * Not setting one will default to the behavior of fetching all the records
 	 * @param maxResults the maximum number of results to retrieve
 	 * @return the spec
diff --git a/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaRetrievingOutboundGatewaySpec.java b/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaRetrievingOutboundGatewaySpec.java
index ef058bca55..d4794ebe6d 100644
--- a/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaRetrievingOutboundGatewaySpec.java
+++ b/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/JpaRetrievingOutboundGatewaySpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -144,10 +144,10 @@ public class JpaRetrievingOutboundGatewaySpec extends JpaBaseOutboundEndpointSpe
 
 	/**
 	 * If not set, this property defaults to <code>false</code>, which means that
-	 * deletion occurs on a per object basis if a collection of entities is being
+	 * deletion occurs on a per-object basis if a collection of entities is being
 	 * deleted.
 	 *<p>If set to 'true' the elements of the payload are deleted as a batch
-	 * operation. Be aware that this exhibits issues in regards to cascaded deletes.
+	 * operation. Be aware that this exhibits issues in regard to cascaded deletes.
 	 *<p>The specification 'JSR 317: Java Persistence API, Version 2.0' does not
 	 * support cascaded deletes in batch operations. The specification states in
 	 * chapter 4.10:
diff --git a/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/package-info.java b/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/package-info.java
index b1c365ffc5..0c03315749 100644
--- a/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/package-info.java
+++ b/spring-integration-jpa/src/main/java/org/springframework/integration/jpa/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides JPA Components support for Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.jpa.dsl;
diff --git a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/AbstractKafkaChannelSpec.java b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/AbstractKafkaChannelSpec.java
index 328aa71c79..c22f000bb3 100644
--- a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/AbstractKafkaChannelSpec.java
+++ b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/AbstractKafkaChannelSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 the original author or authors.
+ * Copyright 2020-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.integration.kafka.dsl;
 
 import org.springframework.integration.dsl.MessageChannelSpec;
 import org.springframework.integration.kafka.channel.AbstractKafkaChannel;
+import org.springframework.lang.Nullable;
 
 /**
  *
@@ -34,10 +35,11 @@ import org.springframework.integration.kafka.channel.AbstractKafkaChannel;
 public abstract class AbstractKafkaChannelSpec<S extends AbstractKafkaChannelSpec<S, C>, C extends AbstractKafkaChannel>
 		extends MessageChannelSpec<S, C> {
 
+	@Nullable
 	protected String groupId; // NOSONAR
 
 	@Override
-	public S id(String idToSet) { // NOSONAR - increase visibility
+	public S id(@Nullable String idToSet) { // NOSONAR - increase visibility
 		return super.id(idToSet);
 	}
 
diff --git a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundChannelAdapterSpec.java b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundChannelAdapterSpec.java
index 9d5dec04fd..ee5d817a93 100644
--- a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundChannelAdapterSpec.java
+++ b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2020 the original author or authors.
+ * Copyright 2018-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,6 +48,7 @@ public class KafkaInboundChannelAdapterSpec<K, V>
 	 */
 	KafkaInboundChannelAdapterSpec(ConsumerFactory<K, V> consumerFactory,
 			ConsumerProperties consumerProperties, boolean allowMultiFetch) {
+
 		this.target = new KafkaMessageSource<>(consumerFactory, consumerProperties, allowMultiFetch);
 	}
 
diff --git a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundGatewaySpec.java b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundGatewaySpec.java
index f06a9d2ec4..6b300ec4e5 100644
--- a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundGatewaySpec.java
+++ b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaInboundGatewaySpec.java
@@ -17,6 +17,7 @@
 package org.springframework.integration.kafka.dsl;
 
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.Map;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
@@ -26,7 +27,6 @@ import org.apache.kafka.common.TopicPartition;
 import org.springframework.integration.dsl.ComponentsRegistration;
 import org.springframework.integration.dsl.MessagingGatewaySpec;
 import org.springframework.integration.kafka.inbound.KafkaInboundGateway;
-import org.springframework.integration.support.ObjectStringMapBuilder;
 import org.springframework.kafka.core.KafkaTemplate;
 import org.springframework.kafka.listener.AbstractMessageListenerContainer;
 import org.springframework.kafka.listener.ConsumerSeekAware;
@@ -164,10 +164,10 @@ public class KafkaInboundGatewaySpec<K, V, R, S extends KafkaInboundGatewaySpec<
 
 		@Override
 		public Map<Object, String> getComponentsToRegister() {
-			return new ObjectStringMapBuilder()
-					.put(this.containerSpec.getObject(), this.containerSpec.getId())
-					.put(this.templateSpec.getObject(), this.templateSpec.getId())
-					.get();
+			Map<Object, String> components = new HashMap<>();
+			components.put(this.containerSpec.getObject(), this.containerSpec.getId());
+			components.put(this.templateSpec.getObject(), this.templateSpec.getId());
+			return components;
 		}
 
 	}
diff --git a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageDrivenChannelAdapterSpec.java b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageDrivenChannelAdapterSpec.java
index 8d3062966d..c6c079cfda 100644
--- a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageDrivenChannelAdapterSpec.java
+++ b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageDrivenChannelAdapterSpec.java
@@ -141,7 +141,7 @@ public class KafkaMessageDrivenChannelAdapterSpec<K, V, S extends KafkaMessageDr
 	}
 
 	/**
-	 * When using a type-aware message converter (such as {@code StringJsonMessageConverter},
+	 * When using a type-aware message converter (such as {@code StringJsonMessageConverter}),
 	 * set the payload type the converter should create. Defaults to {@link Object}.
 	 * @param payloadType the type.
 	 * @return the spec
diff --git a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageListenerContainerSpec.java b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageListenerContainerSpec.java
index 4d839d02f3..072a78b5fb 100644
--- a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageListenerContainerSpec.java
+++ b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaMessageListenerContainerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2022 the original author or authors.
+ * Copyright 2018-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@ import org.springframework.kafka.listener.CommonErrorHandler;
 import org.springframework.kafka.listener.ConcurrentMessageListenerContainer;
 import org.springframework.kafka.listener.ContainerProperties;
 import org.springframework.kafka.support.TopicPartitionOffset;
+import org.springframework.lang.Nullable;
 
 /**
  * A helper class in the Builder pattern style to delegate options to the
@@ -65,7 +66,7 @@ public class KafkaMessageListenerContainerSpec<K, V>
 	}
 
 	@Override
-	public KafkaMessageListenerContainerSpec<K, V> id(String id) { // NOSONAR - increase visibility
+	public KafkaMessageListenerContainerSpec<K, V> id(@Nullable String id) { // NOSONAR - increase visibility
 		return super.id(id);
 	}
 
@@ -205,8 +206,8 @@ public class KafkaMessageListenerContainerSpec<K, V>
 	/**
 	 * Set whether to call consumer.commitSync() or commitAsync() when the
 	 * container is responsible for commits. Default true. See
-	 * https://github.com/spring-projects/spring-kafka/issues/62 At the time of
-	 * writing, async commits are not entirely reliable.
+	 * <a href="https://github.com/spring-projects/spring-kafka/issues/62"/>.
+	 * At the time of writing, async commits are not entirely reliable.
 	 * @param syncCommits true to use commitSync().
 	 * @return the spec.
 	 * @see ContainerProperties#setSyncCommits(boolean)
diff --git a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaTemplateSpec.java b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaTemplateSpec.java
index 0da850faab..2ec42fbc90 100644
--- a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaTemplateSpec.java
+++ b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/KafkaTemplateSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2020 the original author or authors.
+ * Copyright 2018-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import org.springframework.kafka.core.KafkaTemplate;
 import org.springframework.kafka.core.ProducerFactory;
 import org.springframework.kafka.support.ProducerListener;
 import org.springframework.kafka.support.converter.RecordMessageConverter;
+import org.springframework.lang.Nullable;
 
 /**
  * An {@link IntegrationComponentSpec} implementation for the {@link KafkaTemplate}.
@@ -49,7 +50,7 @@ public class KafkaTemplateSpec<K, V>
 	}
 
 	@Override
-	public KafkaTemplateSpec<K, V> id(String id) { // NOSONAR - visibility
+	public KafkaTemplateSpec<K, V> id(@Nullable String id) { // NOSONAR - visibility
 		return super.id(id);
 	}
 
diff --git a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/package-info.java b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/package-info.java
index b70ca47e14..53f5ad837b 100644
--- a/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/package-info.java
+++ b/spring-integration-kafka/src/main/java/org/springframework/integration/kafka/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides Spring Integration Java DSL Components support for Apache Kafka.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.kafka.dsl;
diff --git a/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/Mail.java b/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/Mail.java
index 5870bbb7f2..66e207d80b 100644
--- a/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/Mail.java
+++ b/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/Mail.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2019 the original author or authors.
+ * Copyright 2014-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -115,6 +115,7 @@ public final class Mail {
 	 */
 	public static Pop3MailInboundChannelAdapterSpec pop3InboundAdapter(String host, int port, String username,
 			String password) {
+
 		return new Pop3MailInboundChannelAdapterSpec(host, port, username, password);
 	}
 
@@ -191,7 +192,7 @@ public final class Mail {
 	 * @param charset the charset to use when the default is not appropriate.
 	 * @return the transformer.
 	 */
-	public static MailToStringTransformer toStringTransformer(String charset) {
+	public static MailToStringTransformer toStringTransformer(@Nullable String charset) {
 		MailToStringTransformer transformer = new MailToStringTransformer();
 		if (charset != null) {
 			transformer.setCharset(charset);
diff --git a/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/MailHeadersBuilder.java b/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/MailHeadersBuilder.java
index 4009274cb5..23b3a7403b 100644
--- a/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/MailHeadersBuilder.java
+++ b/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/MailHeadersBuilder.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2019 the original author or authors.
+ * Copyright 2014-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -57,7 +57,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder subjectFunction(Function<Message<P>, String> subject) {
-		return put(MailHeaders.SUBJECT, new FunctionExpression<Message<P>>(subject));
+		return put(MailHeaders.SUBJECT, new FunctionExpression<>(subject));
 	}
 
 	/**
@@ -86,7 +86,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder toFunction(Function<Message<P>, String[]> to) {
-		return put(MailHeaders.TO, new FunctionExpression<Message<P>>(to));
+		return put(MailHeaders.TO, new FunctionExpression<>(to));
 	}
 
 	/**
@@ -115,7 +115,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder ccFunction(Function<Message<P>, String[]> cc) {
-		return put(MailHeaders.CC, new FunctionExpression<Message<P>>(cc));
+		return put(MailHeaders.CC, new FunctionExpression<>(cc));
 	}
 
 	/**
@@ -144,7 +144,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder bccFunction(Function<Message<P>, String[]> bcc) {
-		return put(MailHeaders.BCC, new FunctionExpression<Message<P>>(bcc));
+		return put(MailHeaders.BCC, new FunctionExpression<>(bcc));
 	}
 
 	/**
@@ -157,7 +157,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	}
 
 	/**
-	 * Set the expression that will be evaluated to determine the From: address.
+	 * Set the expression that will be evaluated to determine the {@code From:} address.
 	 * @param from the expression.
 	 * @return the builder.
 	 */
@@ -166,14 +166,14 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	}
 
 	/**
-	 * Set a function that will be invoked to determine the From: address based on the
+	 * Set a function that will be invoked to determine the {@code From:} address based on the
 	 * message.
 	 * @param from the function.
 	 * @param <P> the message payload type.
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder fromFunction(Function<Message<P>, String> from) {
-		return put(MailHeaders.FROM, new FunctionExpression<Message<P>>(from));
+		return put(MailHeaders.FROM, new FunctionExpression<>(from));
 	}
 
 	/**
@@ -202,7 +202,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder replyToFunction(Function<Message<P>, String> replyTo) {
-		return put(MailHeaders.REPLY_TO, new FunctionExpression<Message<P>>(replyTo));
+		return put(MailHeaders.REPLY_TO, new FunctionExpression<>(replyTo));
 	}
 
 	/**
@@ -236,7 +236,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @see org.springframework.mail.javamail.MimeMessageHelper
 	 */
 	public <P> MailHeadersBuilder multipartModeFunction(Function<Message<P>, Integer> multipartMode) {
-		return put(MailHeaders.MULTIPART_MODE, new FunctionExpression<Message<P>>(multipartMode));
+		return put(MailHeaders.MULTIPART_MODE, new FunctionExpression<>(multipartMode));
 	}
 
 	/**
@@ -264,7 +264,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder attachmentFilenameFunction(Function<Message<P>, String> attachmentFilename) {
-		return put(MailHeaders.ATTACHMENT_FILENAME, new FunctionExpression<Message<P>>(attachmentFilename));
+		return put(MailHeaders.ATTACHMENT_FILENAME, new FunctionExpression<>(attachmentFilename));
 	}
 
 	/**
@@ -292,7 +292,7 @@ public class MailHeadersBuilder extends MapBuilder<MailHeadersBuilder, String, O
 	 * @return the builder.
 	 */
 	public <P> MailHeadersBuilder contentTypeFunction(Function<Message<P>, String> contentType) {
-		return put(MailHeaders.CONTENT_TYPE, new FunctionExpression<Message<P>>(contentType));
+		return put(MailHeaders.CONTENT_TYPE, new FunctionExpression<>(contentType));
 	}
 
 	private MailHeadersBuilder putExpression(String key, String expression) {
diff --git a/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/package-info.java b/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/package-info.java
index e15dcb2e9d..d2e39f7120 100644
--- a/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/package-info.java
+++ b/spring-integration-mail/src/main/java/org/springframework/integration/mail/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides Mail Components for the Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.mail.dsl;
diff --git a/spring-integration-mongodb/src/main/java/org/springframework/integration/mongodb/dsl/package-info.java b/spring-integration-mongodb/src/main/java/org/springframework/integration/mongodb/dsl/package-info.java
index 395197955d..8f05105290 100644
--- a/spring-integration-mongodb/src/main/java/org/springframework/integration/mongodb/dsl/package-info.java
+++ b/spring-integration-mongodb/src/main/java/org/springframework/integration/mongodb/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides MongoDB Components support for Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.mongodb.dsl;
diff --git a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/dsl/package-info.java b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/dsl/package-info.java
index 043505dda2..2c264693da 100644
--- a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/dsl/package-info.java
+++ b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/dsl/package-info.java
@@ -2,4 +2,5 @@
  * Provides classes for supporting Java DSL for R2DBC components.
  */
 @org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.r2dbc.dsl;
diff --git a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/R2dbcMessageSource.java b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/R2dbcMessageSource.java
index c4669496a6..e856280d31 100644
--- a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/R2dbcMessageSource.java
+++ b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/R2dbcMessageSource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2022 the original author or authors.
+ * Copyright 2020-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,6 +34,7 @@ import org.springframework.expression.common.LiteralExpression;
 import org.springframework.expression.spel.support.StandardEvaluationContext;
 import org.springframework.integration.endpoint.AbstractMessageSource;
 import org.springframework.integration.expression.ExpressionUtils;
+import org.springframework.lang.Nullable;
 import org.springframework.r2dbc.core.ColumnMapRowMapper;
 import org.springframework.r2dbc.core.DatabaseClient;
 import org.springframework.r2dbc.core.RowsFetchSpec;
@@ -75,10 +76,12 @@ public class R2dbcMessageSource extends AbstractMessageSource<Publisher<?>> {
 
 	private boolean expectSingleResult = false;
 
-	private StandardEvaluationContext evaluationContext;
+	private StandardEvaluationContext evaluationContext = new StandardEvaluationContext();
 
+	@Nullable
 	private String updateSql;
 
+	@Nullable
 	private BiFunction<DatabaseClient.GenericExecuteSpec, Object, DatabaseClient.GenericExecuteSpec> bindFunction;
 
 	private volatile boolean initialized = false;
diff --git a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/package-info.java b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/package-info.java
index 501e1ccd15..339d0f161d 100644
--- a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/package-info.java
+++ b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/inbound/package-info.java
@@ -2,4 +2,5 @@
  * Provides classes for supporting R2DBC inbound components.
  */
 @org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.r2dbc.inbound;
diff --git a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/R2dbcMessageHandler.java b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/R2dbcMessageHandler.java
index 2debbb7232..8cfbe59f41 100644
--- a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/R2dbcMessageHandler.java
+++ b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/R2dbcMessageHandler.java
@@ -56,7 +56,7 @@ public class R2dbcMessageHandler extends AbstractReactiveMessageHandler {
 
 	private final StatementMapper statementMapper;
 
-	private StandardEvaluationContext evaluationContext;
+	private StandardEvaluationContext evaluationContext = new StandardEvaluationContext();
 
 	private Expression queryTypeExpression = new ValueExpression<>(Type.INSERT);
 
@@ -170,7 +170,8 @@ public class R2dbcMessageHandler extends AbstractReactiveMessageHandler {
 
 	private Mono<Void> handleDelete(Message<?> message) {
 		if (this.tableNameExpression != null) {
-			String tableName = evaluateTableNameExpression(message);
+			String tableName = this.tableNameExpression.getValue(this.evaluationContext, message, String.class);
+			Assert.notNull(tableName, "'tableNameExpression' must not evaluate to null");
 			Criteria criteria = evaluateCriteriaExpression(message);
 			StatementMapper.DeleteSpec deleteSpec =
 					this.statementMapper.createDelete(tableName)
@@ -188,7 +189,8 @@ public class R2dbcMessageHandler extends AbstractReactiveMessageHandler {
 
 	private Mono<Void> handleUpdate(Message<?> message) {
 		if (this.tableNameExpression != null) {
-			String tableName = evaluateTableNameExpression(message);
+			String tableName = this.tableNameExpression.getValue(this.evaluationContext, message, String.class);
+			Assert.notNull(tableName, "'tableNameExpression' must not evaluate to null");
 			Map<String, Object> values = evaluateValuesExpression(message);
 			Map<SqlIdentifier, Object> updateMap = transformIntoSqlIdentifierMap(values);
 			Criteria criteria = evaluateCriteriaExpression(message);
@@ -216,7 +218,8 @@ public class R2dbcMessageHandler extends AbstractReactiveMessageHandler {
 	@SuppressWarnings("deprecation")
 	private Mono<Void> handleInsert(Message<?> message) {
 		if (this.tableNameExpression != null) {
-			String tableName = evaluateTableNameExpression(message);
+			String tableName = this.tableNameExpression.getValue(this.evaluationContext, message, String.class);
+			Assert.notNull(tableName, "'tableNameExpression' must not evaluate to null");
 			Map<String, Object> values = evaluateValuesExpression(message);
 
 			StatementMapper.InsertSpec insertSpec = this.statementMapper.createInsert(tableName);
@@ -237,13 +240,6 @@ public class R2dbcMessageHandler extends AbstractReactiveMessageHandler {
 		}
 	}
 
-	private String evaluateTableNameExpression(Message<?> message) {
-		String tableName =
-				this.tableNameExpression.getValue(this.evaluationContext, message, String.class); // NOSONAR
-		Assert.notNull(tableName, "'tableNameExpression' must not evaluate to null");
-		return tableName;
-	}
-
 	@SuppressWarnings("unchecked")
 	private Map<String, Object> evaluateValuesExpression(Message<?> message) {
 		Assert.notNull(this.valuesExpression,
diff --git a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/package-info.java b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/package-info.java
index 20c7e8a1b0..ebe2b74222 100644
--- a/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/package-info.java
+++ b/spring-integration-r2dbc/src/main/java/org/springframework/integration/r2dbc/outbound/package-info.java
@@ -2,4 +2,5 @@
  * Provides classes for supporting R2DBC outbound components.
  */
 @org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.r2dbc.outbound;
diff --git a/spring-integration-rsocket/src/main/java/org/springframework/integration/rsocket/dsl/package-info.java b/spring-integration-rsocket/src/main/java/org/springframework/integration/rsocket/dsl/package-info.java
index 28166a8732..a2cfe7f362 100644
--- a/spring-integration-rsocket/src/main/java/org/springframework/integration/rsocket/dsl/package-info.java
+++ b/spring-integration-rsocket/src/main/java/org/springframework/integration/rsocket/dsl/package-info.java
@@ -2,4 +2,5 @@
  * Provides RSocket Components support for Spring Integration Java DSL.
  */
 @org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.rsocket.dsl;
diff --git a/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/DslScriptExecutingMessageProcessor.java b/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/DslScriptExecutingMessageProcessor.java
index 292899b0f7..386502c307 100644
--- a/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/DslScriptExecutingMessageProcessor.java
+++ b/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/DslScriptExecutingMessageProcessor.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -38,7 +38,7 @@ import org.springframework.util.StringUtils;
  * The adapter {@link MessageProcessor} around {@link AbstractScriptExecutingMessageProcessor}.
  * Delegates to the {@code GroovyScriptExecutingMessageProcessor}, if provided {@link #lang}
  * matches to {@code groovy} string and {@code spring-integration-groovy} jar is in classpath.
- * Otherwise to the {@link ScriptExecutingMessageProcessor}.
+ * Otherwise, to the {@link ScriptExecutingMessageProcessor}.
  *
  * @author Artem Bilan
  *
diff --git a/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/ScriptSpec.java b/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/ScriptSpec.java
index 513ee86cc6..04ad106eb5 100644
--- a/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/ScriptSpec.java
+++ b/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/ScriptSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -40,7 +40,7 @@ public class ScriptSpec extends MessageProcessorSpec<ScriptSpec> {
 
 	private ScriptVariableGenerator variableGenerator;
 
-	private Map<String, Object> variables = new HashMap<String, Object>();
+	private final Map<String, Object> variables = new HashMap<>();
 
 	ScriptSpec(Resource scriptResource) {
 		Assert.notNull(scriptResource, "'scriptResource' must not be null");
diff --git a/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/package-info.java b/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/package-info.java
index 625b5db41f..f6ef9725d3 100644
--- a/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/package-info.java
+++ b/spring-integration-scripting/src/main/java/org/springframework/integration/scripting/dsl/package-info.java
@@ -1,4 +1,5 @@
 /**
  * Provides Scripting Components support for Spring Integration Java DSL.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.integration.scripting.dsl;
diff --git a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/Sftp.java b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/Sftp.java
index 9a2a9540a8..f588aff130 100644
--- a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/Sftp.java
+++ b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/Sftp.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2022 the original author or authors.
+ * Copyright 2014-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,7 @@ import org.springframework.integration.file.remote.session.SessionFactory;
 import org.springframework.integration.file.support.FileExistsMode;
 import org.springframework.integration.sftp.gateway.SftpOutboundGateway;
 import org.springframework.integration.sftp.session.SftpRemoteFileTemplate;
+import org.springframework.lang.Nullable;
 
 /**
  * The factory for SFTP components.
@@ -56,7 +57,7 @@ public final class Sftp {
 	 * @return the spec.
 	 */
 	public static SftpInboundChannelAdapterSpec inboundAdapter(SessionFactory<SftpClient.DirEntry> sessionFactory,
-			Comparator<File> receptionOrderComparator) {
+			@Nullable Comparator<File> receptionOrderComparator) {
 
 		return new SftpInboundChannelAdapterSpec(sessionFactory, receptionOrderComparator);
 	}
@@ -82,7 +83,7 @@ public final class Sftp {
 	 */
 	public static SftpStreamingInboundChannelAdapterSpec inboundStreamingAdapter(
 			RemoteFileTemplate<SftpClient.DirEntry> remoteFileTemplate,
-			Comparator<SftpClient.DirEntry> receptionOrderComparator) {
+			@Nullable Comparator<SftpClient.DirEntry> receptionOrderComparator) {
 
 		return new SftpStreamingInboundChannelAdapterSpec(remoteFileTemplate, receptionOrderComparator);
 	}
diff --git a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpInboundChannelAdapterSpec.java b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpInboundChannelAdapterSpec.java
index e3a9ccfb76..204414c2ee 100644
--- a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpInboundChannelAdapterSpec.java
+++ b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2022 the original author or authors.
+ * Copyright 2014-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,6 +31,7 @@ import org.springframework.integration.sftp.filters.SftpRegexPatternFileListFilt
 import org.springframework.integration.sftp.filters.SftpSimplePatternFileListFilter;
 import org.springframework.integration.sftp.inbound.SftpInboundFileSynchronizer;
 import org.springframework.integration.sftp.inbound.SftpInboundFileSynchronizingMessageSource;
+import org.springframework.lang.Nullable;
 
 /**
  * A {@link RemoteFileInboundChannelAdapterSpec} for an {@link SftpInboundFileSynchronizingMessageSource}.
@@ -44,7 +45,7 @@ public class SftpInboundChannelAdapterSpec
 		SftpInboundFileSynchronizingMessageSource> {
 
 	protected SftpInboundChannelAdapterSpec(SessionFactory<SftpClient.DirEntry> sessionFactory,
-			Comparator<File> comparator) {
+			@Nullable Comparator<File> comparator) {
 
 		super(new SftpInboundFileSynchronizer(sessionFactory));
 		this.target = new SftpInboundFileSynchronizingMessageSource(this.synchronizer, comparator);
diff --git a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpStreamingInboundChannelAdapterSpec.java b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpStreamingInboundChannelAdapterSpec.java
index 99c51d2409..fbfcb10213 100644
--- a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpStreamingInboundChannelAdapterSpec.java
+++ b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/SftpStreamingInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import org.springframework.integration.sftp.filters.SftpPersistentAcceptOnceFile
 import org.springframework.integration.sftp.filters.SftpRegexPatternFileListFilter;
 import org.springframework.integration.sftp.filters.SftpSimplePatternFileListFilter;
 import org.springframework.integration.sftp.inbound.SftpStreamingMessageSource;
+import org.springframework.lang.Nullable;
 
 /**
  * @author Gary Russell
@@ -41,7 +42,7 @@ public class SftpStreamingInboundChannelAdapterSpec
 		SftpStreamingInboundChannelAdapterSpec, SftpStreamingMessageSource> {
 
 	protected SftpStreamingInboundChannelAdapterSpec(RemoteFileTemplate<SftpClient.DirEntry> remoteFileTemplate,
-			Comparator<SftpClient.DirEntry> comparator) {
+			@Nullable Comparator<SftpClient.DirEntry> comparator) {
 
 		this.target = new SftpStreamingMessageSource(remoteFileTemplate, comparator);
 	}
diff --git a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/package-info.java b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/package-info.java
index 1e1064951a..d17169b3ed 100644
--- a/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/package-info.java
+++ b/spring-integration-sftp/src/main/java/org/springframework/integration/sftp/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides SFTP Components for the Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.sftp.dsl;
diff --git a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/Smb.java b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/Smb.java
index 386978535d..0bbce68f0b 100644
--- a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/Smb.java
+++ b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/Smb.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,11 +28,13 @@ import org.springframework.integration.file.remote.session.SessionFactory;
 import org.springframework.integration.file.support.FileExistsMode;
 import org.springframework.integration.smb.outbound.SmbOutboundGateway;
 import org.springframework.integration.smb.session.SmbRemoteFileTemplate;
+import org.springframework.lang.Nullable;
 
 /**
  * The factory for SMB components.
  *
  * @author Gregory Bragg
+ * @author Artem Bilan
  *
  * @since 6.0
  */
@@ -54,7 +56,7 @@ public final class Smb {
 	 * @return the spec.
 	 */
 	public static SmbInboundChannelAdapterSpec inboundAdapter(SessionFactory<SmbFile> sessionFactory,
-			Comparator<File> receptionOrderComparator) {
+			@Nullable Comparator<File> receptionOrderComparator) {
 
 		return new SmbInboundChannelAdapterSpec(sessionFactory, receptionOrderComparator);
 	}
@@ -80,7 +82,7 @@ public final class Smb {
 	 */
 	public static SmbStreamingInboundChannelAdapterSpec inboundStreamingAdapter(
 			RemoteFileTemplate<SmbFile> remoteFileTemplate,
-			Comparator<SmbFile> receptionOrderComparator) {
+			@Nullable Comparator<SmbFile> receptionOrderComparator) {
 
 		return new SmbStreamingInboundChannelAdapterSpec(remoteFileTemplate, receptionOrderComparator);
 	}
diff --git a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbInboundChannelAdapterSpec.java b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbInboundChannelAdapterSpec.java
index c7990d97ec..5605fa340d 100644
--- a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbInboundChannelAdapterSpec.java
+++ b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -31,11 +31,13 @@ import org.springframework.integration.smb.filters.SmbRegexPatternFileListFilter
 import org.springframework.integration.smb.filters.SmbSimplePatternFileListFilter;
 import org.springframework.integration.smb.inbound.SmbInboundFileSynchronizer;
 import org.springframework.integration.smb.inbound.SmbInboundFileSynchronizingMessageSource;
+import org.springframework.lang.Nullable;
 
 /**
  * A {@link RemoteFileInboundChannelAdapterSpec} for an {@link SmbInboundFileSynchronizingMessageSource}.
  *
  * @author Gregory Bragg
+ * @author Artem Bilan
  *
  * @since 6.0
  */
@@ -43,7 +45,9 @@ public class SmbInboundChannelAdapterSpec
 		extends RemoteFileInboundChannelAdapterSpec<SmbFile, SmbInboundChannelAdapterSpec,
 		SmbInboundFileSynchronizingMessageSource> {
 
-	protected SmbInboundChannelAdapterSpec(SessionFactory<SmbFile> sessionFactory, Comparator<File> comparator) {
+	protected SmbInboundChannelAdapterSpec(SessionFactory<SmbFile> sessionFactory,
+			@Nullable Comparator<File> comparator) {
+
 		super(new SmbInboundFileSynchronizer(sessionFactory));
 		this.target = new SmbInboundFileSynchronizingMessageSource(this.synchronizer, comparator);
 	}
diff --git a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbStreamingInboundChannelAdapterSpec.java b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbStreamingInboundChannelAdapterSpec.java
index 4768f2bd76..d3fca1737c 100644
--- a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbStreamingInboundChannelAdapterSpec.java
+++ b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/SmbStreamingInboundChannelAdapterSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,11 +29,13 @@ import org.springframework.integration.smb.filters.SmbPersistentAcceptOnceFileLi
 import org.springframework.integration.smb.filters.SmbRegexPatternFileListFilter;
 import org.springframework.integration.smb.filters.SmbSimplePatternFileListFilter;
 import org.springframework.integration.smb.inbound.SmbStreamingMessageSource;
+import org.springframework.lang.Nullable;
 
 /**
  * A {@link RemoteFileStreamingInboundChannelAdapterSpec} for a {@link SmbStreamingMessageSource}.
  *
  * @author Gregory Bragg
+ * @author Artem Bilan
  *
  * @since 6.0
  */
@@ -42,7 +44,7 @@ public class SmbStreamingInboundChannelAdapterSpec
 		SmbStreamingMessageSource> {
 
 	protected SmbStreamingInboundChannelAdapterSpec(RemoteFileTemplate<SmbFile> remoteFileTemplate,
-			Comparator<SmbFile> comparator) {
+			@Nullable Comparator<SmbFile> comparator) {
 
 		this.target = new SmbStreamingMessageSource(remoteFileTemplate, comparator);
 	}
diff --git a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/package-info.java b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/package-info.java
index 58576b42ef..bf53725827 100644
--- a/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/package-info.java
+++ b/spring-integration-smb/src/main/java/org/springframework/integration/smb/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides SMB Components for the Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.smb.dsl;
diff --git a/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFlux.java b/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFlux.java
index 707d77c5d1..1ffcbd64d7 100644
--- a/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFlux.java
+++ b/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFlux.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2019 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import java.util.function.Function;
 import org.springframework.expression.Expression;
 import org.springframework.integration.expression.FunctionExpression;
 import org.springframework.integration.webflux.inbound.WebFluxInboundEndpoint;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.web.reactive.function.client.WebClient;
 
@@ -82,7 +83,7 @@ public final class WebFlux {
 	 * @param webClient {@link WebClient} to use.
 	 * @return the WebFluxMessageHandlerSpec instance
 	 */
-	public static WebFluxMessageHandlerSpec outboundChannelAdapter(URI uri, WebClient webClient) {
+	public static WebFluxMessageHandlerSpec outboundChannelAdapter(URI uri, @Nullable WebClient webClient) {
 		return new WebFluxMessageHandlerSpec(uri, webClient)
 				.expectReply(false);
 	}
@@ -94,7 +95,7 @@ public final class WebFlux {
 	 * @param webClient {@link WebClient} to use.
 	 * @return the WebFluxMessageHandlerSpec instance
 	 */
-	public static WebFluxMessageHandlerSpec outboundChannelAdapter(String uri, WebClient webClient) {
+	public static WebFluxMessageHandlerSpec outboundChannelAdapter(String uri, @Nullable WebClient webClient) {
 		return new WebFluxMessageHandlerSpec(uri, webClient)
 				.expectReply(false);
 	}
@@ -123,7 +124,7 @@ public final class WebFlux {
 	 * @return the WebFluxMessageHandlerSpec instance
 	 */
 	public static WebFluxMessageHandlerSpec outboundChannelAdapter(Expression uriExpression,
-			WebClient webClient) {
+			@Nullable WebClient webClient) {
 
 		return new WebFluxMessageHandlerSpec(uriExpression, webClient)
 				.expectReply(false);
@@ -177,7 +178,7 @@ public final class WebFlux {
 	 * @param webClient {@link WebClient} to use.
 	 * @return the WebFluxMessageHandlerSpec instance
 	 */
-	public static WebFluxMessageHandlerSpec outboundGateway(URI uri, WebClient webClient) {
+	public static WebFluxMessageHandlerSpec outboundGateway(URI uri, @Nullable WebClient webClient) {
 		return new WebFluxMessageHandlerSpec(uri, webClient);
 	}
 
@@ -188,7 +189,7 @@ public final class WebFlux {
 	 * @param webClient {@link WebClient} to use.
 	 * @return the WebFluxMessageHandlerSpec instance
 	 */
-	public static WebFluxMessageHandlerSpec outboundGateway(String uri, WebClient webClient) {
+	public static WebFluxMessageHandlerSpec outboundGateway(String uri, @Nullable WebClient webClient) {
 		return new WebFluxMessageHandlerSpec(uri, webClient);
 	}
 
@@ -202,7 +203,7 @@ public final class WebFlux {
 	 * @return the WebFluxMessageHandlerSpec instance
 	 */
 	public static <P> WebFluxMessageHandlerSpec outboundGateway(Function<Message<P>, ?> uriFunction,
-			WebClient webClient) {
+			@Nullable WebClient webClient) {
 
 		return outboundGateway(new FunctionExpression<>(uriFunction), webClient);
 	}
@@ -216,7 +217,7 @@ public final class WebFlux {
 	 * @return the WebFluxMessageHandlerSpec instance
 	 */
 	public static WebFluxMessageHandlerSpec outboundGateway(Expression uriExpression,
-			WebClient webClient) {
+			@Nullable WebClient webClient) {
 
 		return new WebFluxMessageHandlerSpec(uriExpression, webClient);
 	}
diff --git a/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFluxMessageHandlerSpec.java b/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFluxMessageHandlerSpec.java
index b6a9a99b06..7e907bf641 100644
--- a/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFluxMessageHandlerSpec.java
+++ b/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/WebFluxMessageHandlerSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2021 the original author or authors.
+ * Copyright 2017-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import org.springframework.integration.expression.FunctionExpression;
 import org.springframework.integration.expression.ValueExpression;
 import org.springframework.integration.http.dsl.BaseHttpMessageHandlerSpec;
 import org.springframework.integration.webflux.outbound.WebFluxRequestExecutingMessageHandler;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.web.reactive.function.BodyExtractor;
 import org.springframework.web.reactive.function.client.WebClient;
@@ -46,17 +47,18 @@ import org.springframework.web.reactive.function.client.WebClient;
 public class WebFluxMessageHandlerSpec
 		extends BaseHttpMessageHandlerSpec<WebFluxMessageHandlerSpec, WebFluxRequestExecutingMessageHandler> {
 
+	@Nullable
 	protected final WebClient webClient; // NOSONAR - final
 
-	protected WebFluxMessageHandlerSpec(URI uri, WebClient webClient) {
+	protected WebFluxMessageHandlerSpec(URI uri, @Nullable WebClient webClient) {
 		this(new ValueExpression<>(uri), webClient);
 	}
 
-	protected WebFluxMessageHandlerSpec(String uri, WebClient webClient) {
+	protected WebFluxMessageHandlerSpec(String uri, @Nullable WebClient webClient) {
 		this(new LiteralExpression(uri), webClient);
 	}
 
-	protected WebFluxMessageHandlerSpec(Expression uriExpression, WebClient webClient) {
+	protected WebFluxMessageHandlerSpec(Expression uriExpression, @Nullable WebClient webClient) {
 		super(new WebFluxRequestExecutingMessageHandler(uriExpression, webClient));
 		this.webClient = webClient;
 	}
diff --git a/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/package-info.java b/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/package-info.java
index 965db424f4..961f399976 100644
--- a/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/package-info.java
+++ b/spring-integration-webflux/src/main/java/org/springframework/integration/webflux/dsl/package-info.java
@@ -1,4 +1,6 @@
 /**
  * Provides WebFlux Components support for Spring Integration Java DSL.
  */
+@org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.webflux.dsl;
diff --git a/spring-integration-ws/src/main/java/org/springframework/integration/ws/SimpleWebServiceOutboundGateway.java b/spring-integration-ws/src/main/java/org/springframework/integration/ws/SimpleWebServiceOutboundGateway.java
index 42f16e2391..5481b2dd31 100644
--- a/spring-integration-ws/src/main/java/org/springframework/integration/ws/SimpleWebServiceOutboundGateway.java
+++ b/spring-integration-ws/src/main/java/org/springframework/integration/ws/SimpleWebServiceOutboundGateway.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import javax.xml.transform.dom.DOMSource;
 
 import org.w3c.dom.Document;
 
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessagingException;
 import org.springframework.util.Assert;
@@ -65,7 +66,8 @@ public class SimpleWebServiceOutboundGateway extends AbstractWebServiceOutboundG
 		this(destinationProvider, sourceExtractor, null);
 	}
 
-	public SimpleWebServiceOutboundGateway(DestinationProvider destinationProvider, SourceExtractor<?> sourceExtractor,
+	public SimpleWebServiceOutboundGateway(DestinationProvider destinationProvider,
+			@Nullable SourceExtractor<?> sourceExtractor,
 			WebServiceMessageFactory messageFactory) {
 
 		super(destinationProvider, messageFactory);
@@ -80,7 +82,7 @@ public class SimpleWebServiceOutboundGateway extends AbstractWebServiceOutboundG
 		this(uri, sourceExtractor, null);
 	}
 
-	public SimpleWebServiceOutboundGateway(String uri, SourceExtractor<?> sourceExtractor,
+	public SimpleWebServiceOutboundGateway(String uri, @Nullable SourceExtractor<?> sourceExtractor,
 			WebServiceMessageFactory messageFactory) {
 
 		super(uri, messageFactory);
diff --git a/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/SimpleWsOutboundGatewaySpec.java b/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/SimpleWsOutboundGatewaySpec.java
index 92ce200669..4560a6345f 100644
--- a/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/SimpleWsOutboundGatewaySpec.java
+++ b/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/SimpleWsOutboundGatewaySpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2021 the original author or authors.
+ * Copyright 2020-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.util.Arrays;
 
 import org.springframework.integration.JavaUtils;
 import org.springframework.integration.ws.SimpleWebServiceOutboundGateway;
+import org.springframework.lang.Nullable;
 import org.springframework.ws.WebServiceMessageFactory;
 import org.springframework.ws.client.core.FaultMessageResolver;
 import org.springframework.ws.client.core.SourceExtractor;
@@ -39,6 +40,7 @@ import org.springframework.ws.transport.WebServiceMessageSender;
 public class SimpleWsOutboundGatewaySpec
 		extends BaseWsOutboundGatewaySpec<SimpleWsOutboundGatewaySpec, SimpleWebServiceOutboundGateway> {
 
+	@Nullable
 	protected SourceExtractor<?> sourceExtractor; // NOSONAR
 
 	protected SimpleWsOutboundGatewaySpec(WebServiceTemplate template) {
diff --git a/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/package-info.java b/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/package-info.java
index b2fce402d2..b10046610d 100644
--- a/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/package-info.java
+++ b/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/package-info.java
@@ -1,4 +1,5 @@
 /**
  * Contains classes for DSL support.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.integration.ws.dsl;
diff --git a/spring-integration-zeromq/src/main/java/org/springframework/integration/zeromq/dsl/package-info.java b/spring-integration-zeromq/src/main/java/org/springframework/integration/zeromq/dsl/package-info.java
index cfb4e53cfa..5fd970e23a 100644
--- a/spring-integration-zeromq/src/main/java/org/springframework/integration/zeromq/dsl/package-info.java
+++ b/spring-integration-zeromq/src/main/java/org/springframework/integration/zeromq/dsl/package-info.java
@@ -2,4 +2,5 @@
  * Provides classes for supporting ZeroMQ component via Java DSL.
  */
 @org.springframework.lang.NonNullApi
+@org.springframework.lang.NonNullFields
 package org.springframework.integration.zeromq.dsl;