Fixed README generation and polished few tests

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistry.java

@@ -430,6 +430,7 @@ public class BeanFactoryAwareFunctionRegistry
 				}
 			}
 
+			// Outputs will be converted only if we're told how (via  acceptedOutputMimeTypes), otherwise output returned as is.
 			if (!ObjectUtils.isEmpty(this.acceptedOutputMimeTypes)) {
 				result = result instanceof Publisher
 						? this.convertOutputPublisherIfNecessary((Publisher<?>) result, this.acceptedOutputMimeTypes)
@@ -462,7 +463,7 @@ public class BeanFactoryAwareFunctionRegistry
 				}
 				convertedValue = Tuples.fromArray(convertedInputArray);
 			}
-			else {
+			else if (value != null) {
 				List<MimeType> acceptedContentTypes = MimeTypeUtils.parseMimeTypes(acceptedOutputMimeTypes[0].toString());
 
 				convertedValue = acceptedContentTypes.stream()

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistryTests.java

@@ -40,6 +40,7 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.support.GenericMessage;
 import org.springframework.messaging.support.MessageBuilder;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -78,6 +79,28 @@ public class BeanFactoryAwareFunctionRegistryTests {
 		assertThat(messageResult.get(1).getPayload()).isEqualTo("\"UPPERCASEFLUX2\"".getBytes(StandardCharsets.UTF_8));
 	}
 
+	@Test
+	public void testConsumerFunction() { // function that returns Void, effectively a Consumer
+		FunctionCatalog catalog = this.configureCatalog();
+
+		Function<String, Void> consumerFunction = catalog.lookup("consumerFunction");
+		assertThat(consumerFunction.apply("hello")).isNull();
+
+		Function<Message<byte[]>, Void> consumerFunctionAsMessageA = catalog.lookup("consumerFunction");
+		assertThat(consumerFunctionAsMessageA.apply(new GenericMessage<byte[]>("\"hello\"".getBytes()))).isNull();
+
+		Function<Message<byte[]>, Void> consumerFunctionAsMessageB = catalog.lookup("consumerFunction", "application/json");
+		assertThat(consumerFunctionAsMessageB.apply(new GenericMessage<byte[]>("\"hello\"".getBytes()))).isNull();
+	}
+
+	@Test
+	public void testMessageToPojoConversion() {
+		FunctionCatalog catalog = this.configureCatalog();
+		Function<Message<String>, Person> uppercasePerson = catalog.lookup("uppercasePerson");
+		Person person =  uppercasePerson.apply(MessageBuilder.withPayload("{\"name\":\"bill\",\"id\":2}").build());
+		assertThat(person.getName()).isEqualTo("BILL");
+	}
+
 	/*
 	 * When invoking imperative function as reactive the rules are
 	 * - the input wrapper must match the output wrapper (e.g., <Flux, Flux> or <Mono, Mono>)
@@ -249,6 +272,13 @@ public class BeanFactoryAwareFunctionRegistryTests {
 	@Configuration
 	protected static class SampleFunctionConfiguration {
 
+		@Bean
+		public Function<Person, Person> uppercasePerson() {
+			return person -> {
+				return new Person(person.getName().toUpperCase(), person.getId());
+			};
+		}
+
 		@Bean
 		public Supplier<String> numberword() {
 			return () -> "one";
@@ -267,6 +297,14 @@ public class BeanFactoryAwareFunctionRegistryTests {
 			return v -> v.toUpperCase();
 		}
 
+		@Bean
+		public Function<String, Void> consumerFunction() {
+			return v -> {
+				System.out.println("Value: " + v);
+				return null;
+			};
+		}
+
 		@Bean
 		public Function<Flux<String>, Flux<String>> uppercaseFlux() {
 			return flux -> flux.map(v -> v.toUpperCase());
@@ -392,10 +430,13 @@ public class BeanFactoryAwareFunctionRegistryTests {
 		}
 	}
 
-	private static class Person {
+	public static class Person {
 		private String name;
 		private int id;
-		Person(String name, int id) {
+		public Person() {
+
+		}
+		public Person(String name, int id) {
 			this.name = name;
 			this.id = id;
 		}