* Add meaningful exception when no function definition in catalog

spring-cloud-function-integration/src/main/java/org/springframework/cloud/function/integration/dsl/FunctionLookupHelper.java

@@ -23,6 +23,7 @@ import java.util.function.Function;
 import java.util.function.Supplier;
 
 import org.springframework.cloud.function.context.FunctionCatalog;
+import org.springframework.util.Assert;
 
 /**
  * The helper class to lookup functions from the catalog in lazy manner and cache their instances.
@@ -55,7 +56,13 @@ public class FunctionLookupHelper {
 	}
 
 	private <T> Supplier<T> lazyLookup(Class<?> functionType, String functionDefinition) {
-		return memoize(() -> this.functionCatalog.lookup(functionType, functionDefinition));
+		return memoize(() -> requireNonNull(functionType, functionDefinition));
+	}
+
+	private  <T> T requireNonNull(Class<?> functionType, String functionDefinition) {
+		T function = this.functionCatalog.lookup(functionType, functionDefinition);
+		Assert.notNull(function, () -> "No '" + functionDefinition + "' in the catalog");
+		return function;
 	}
 
 	/**
@@ -72,7 +79,7 @@ public class FunctionLookupHelper {
 				synchronized (value) {
 					val = value.get();
 					if (val == null) {
-						val = Objects.requireNonNull(delegate.get());
+						val = delegate.get();
 						value.set(val);
 					}
 				}

spring-cloud-function-integration/src/test/java/org/springframework/cloud/function/integration/dsl/FunctionFlowTests.java

@@ -36,16 +36,19 @@ import org.springframework.integration.channel.QueueChannel;
 import org.springframework.integration.dsl.IntegrationFlow;
 import org.springframework.integration.dsl.PollerSpec;
 import org.springframework.integration.dsl.Pollers;
+import org.springframework.integration.dsl.context.IntegrationFlowContext;
 import org.springframework.integration.endpoint.SourcePollingChannelAdapter;
 import org.springframework.integration.handler.LoggingHandler;
 import org.springframework.integration.scheduling.PollerMetadata;
 import org.springframework.integration.test.util.OnlyOnceTrigger;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
+import org.springframework.messaging.MessageDeliveryException;
 import org.springframework.messaging.support.GenericMessage;
 import org.springframework.test.annotation.DirtiesContext;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.mockito.Mockito.verify;
 
 /**
@@ -98,6 +101,27 @@ public class FunctionFlowTests {
 		verify(this.functionCatalog).lookup(Consumer.class, "upperCaseFunction|simpleStringConsumer");
 	}
 
+	@Test
+	void noFunctionInCatalogException(@Autowired FunctionFlowBuilder functionFlowBuilder,
+			@Autowired IntegrationFlowContext integrationFlowContext) {
+
+		IntegrationFlow wrongFlow =
+				functionFlowBuilder.from("inputChannel")
+						.accept("nonExistingConsumer");
+
+		IntegrationFlowContext.IntegrationFlowRegistration registration =
+				integrationFlowContext.registration(wrongFlow)
+						.register();
+
+		assertThatExceptionOfType(MessageDeliveryException.class)
+				.isThrownBy(() -> registration.getInputChannel().send(new GenericMessage<>("test")))
+				.withRootCauseInstanceOf(IllegalArgumentException.class)
+				.withStackTraceContaining("No 'nonExistingConsumer' in the catalog");
+
+		registration.destroy();
+	}
+
+
 	@EnableAutoConfiguration
 	@Configuration(proxyBeanMethods = false)
 	static class TestIntegrationConfiguration {