GH-10083: Migrate spring-integration-camel to JSpecify Nullable

Related to: https://github.com/spring-projects/spring-integration/issues/10083

This change is applicable only to `spring-integration-camel`.

*Replaced `org.springframework.lang.Nullable` with `org.jspecify.annotations.Nullable`.
* Handled changes in `package-info.java`
* Handled nullable related issues in `CamelMessageHandler`.

Fixed issues in `CamelMessageHandler` as per review comments (suppressed warnings for `NullAway.Init` so that `Objects.requireNonNull` is not needed).

Signed-off-by: Anayonkar Shivalkar <anayonkar.shivalkar@gmail.com>

spring-integration-camel/src/main/java/org/springframework/integration/camel/dsl/Camel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022-2024 the original author or authors.
+ * Copyright 2022-2025 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.
@@ -19,8 +19,7 @@ package org.springframework.integration.camel.dsl;
 import org.apache.camel.ExchangePattern;
 import org.apache.camel.ProducerTemplate;
 import org.apache.camel.builder.LambdaRouteBuilder;
-
-import org.springframework.lang.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Factory class for Apache Camel components DSL.

spring-integration-camel/src/main/java/org/springframework/integration/camel/dsl/CamelMessageHandlerSpec.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2025 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.apache.camel.ExchangePattern;
 import org.apache.camel.ProducerTemplate;
 import org.apache.camel.builder.LambdaRouteBuilder;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.expression.Expression;
 import org.springframework.integration.camel.outbound.CamelMessageHandler;
@@ -30,7 +31,6 @@ import org.springframework.integration.camel.support.CamelHeaderMapper;
 import org.springframework.integration.dsl.MessageHandlerSpec;
 import org.springframework.integration.expression.FunctionExpression;
 import org.springframework.integration.mapping.HeaderMapper;
-import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 

spring-integration-camel/src/main/java/org/springframework/integration/camel/dsl/package-info.java

@@ -2,6 +2,5 @@
  * Provides supporting classes for JavaDSL with Apache Camel components.
  */
 
-@org.springframework.lang.NonNullApi
-@org.springframework.lang.NonNullFields
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.camel.dsl;

spring-integration-camel/src/main/java/org/springframework/integration/camel/outbound/CamelMessageHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2025 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.apache.camel.ProducerTemplate;
 import org.apache.camel.builder.LambdaRouteBuilder;
 import org.apache.camel.builder.RouteBuilder;
 import org.apache.camel.model.RouteDefinition;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanInitializationException;
@@ -40,7 +41,6 @@ import org.springframework.integration.expression.ValueExpression;
 import org.springframework.integration.handler.AbstractReplyProducingMessageHandler;
 import org.springframework.integration.mapping.HeaderMapper;
 import org.springframework.integration.support.AbstractIntegrationMessageBuilder;
-import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -68,6 +68,7 @@ import org.springframework.util.StringUtils;
  */
 public class CamelMessageHandler extends AbstractReplyProducingMessageHandler {
 
+	@SuppressWarnings("NullAway.Init")
 	private ProducerTemplate producerTemplate;
 
 	private Expression exchangePatternExpression = new ValueExpression<>(ExchangePattern.InOnly);
@@ -83,6 +84,7 @@ public class CamelMessageHandler extends AbstractReplyProducingMessageHandler {
 	@Nullable
 	private Expression exchangePropertiesExpression;
 
+	@SuppressWarnings("NullAway.Init")
 	private StandardEvaluationContext evaluationContext;
 
 	public CamelMessageHandler() {
@@ -197,6 +199,7 @@ public class CamelMessageHandler extends AbstractReplyProducingMessageHandler {
 	}
 
 	@Override
+	@Nullable
 	protected Object handleRequestMessage(Message<?> requestMessage) {
 		ExchangePattern exchangePattern =
 				this.exchangePatternExpression.getValue(this.evaluationContext, requestMessage, ExchangePattern.class);

spring-integration-camel/src/main/java/org/springframework/integration/camel/outbound/package-info.java

@@ -2,6 +2,5 @@
  * Provides classes for Apache Camel outbound channel adapters.
  */
 
-@org.springframework.lang.NonNullApi
-@org.springframework.lang.NonNullFields
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.camel.outbound;

spring-integration-camel/src/main/java/org/springframework/integration/camel/support/package-info.java

@@ -2,6 +2,5 @@
  * Provides supporting classes for Apache Camel channel adapters.
  */
 
-@org.springframework.lang.NonNullApi
-@org.springframework.lang.NonNullFields
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.camel.support;