FunctionTypeUtils test for NPE

Related to https://stackoverflow.com/questions/72163534/spring-batch-integration-throwns-org-springframework-messaging-messagehandlingex

The `FunctionTypeUtils.isMessage()` fails with NPE
when target method has non-message argument with generic parameter.
Even if we instantiate the class with specific generic argument,
that info is not available for reflection and `MethodParameter`
end up with a generic parameter name which is essentially a `TypeVariable`

The stacktrace is like this:
```
java.lang.NullPointerException: Cannot invoke "java.lang.Class.getGenericInterfaces()" because "targetType" is null

	at net.jodah.typetools.TypeResolver.getTypeVariableMap(TypeResolver.java:494)
	at net.jodah.typetools.TypeResolver.resolveRawClass(TypeResolver.java:387)
	at net.jodah.typetools.TypeResolver.resolveRawClass(TypeResolver.java:373)
	at org.springframework.cloud.function.context.catalog.FunctionTypeUtils.isMessage(FunctionTypeUtils.java:416)
```

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

@@ -17,10 +17,13 @@
 package org.springframework.cloud.function.context.catalog;
 
 
+import java.lang.reflect.Method;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
+import java.util.Date;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Supplier;
@@ -31,8 +34,10 @@ import reactor.core.publisher.Mono;
 import reactor.util.function.Tuple2;
 import reactor.util.function.Tuple3;
 
+import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.messaging.Message;
+import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -42,7 +47,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  *
  */
 @SuppressWarnings("unused")
-public class FunctionTypeUtilsTests {
+public class FunctionTypeUtilsTests<T> {
 
 	@Test
 	public void testFunctionTypeFrom() throws Exception {
@@ -147,6 +152,21 @@ public class FunctionTypeUtilsTests {
 		assertThat(FunctionTypeUtils.isTypeCollection(new ParameterizedTypeReference<Flux<Message<List<String>>>>() { }.getType())).isFalse();
 	}
 
+	@Test
+	public void testNoNpeFromIsMessage() {
+		FunctionTypeUtilsTests<Date> testService = new FunctionTypeUtilsTests<>();
+
+		Method methodUnderTest =
+			ReflectionUtils.findMethod(testService.getClass(), "notAMessageMethod", AtomicReference.class);
+		MethodParameter methodParameter = MethodParameter.forExecutable(methodUnderTest, 0);
+
+		assertThat(FunctionTypeUtils.isMessage(methodParameter.getGenericParameterType())).isFalse();
+	}
+
+	void notAMessageMethod(AtomicReference<T> payload) {
+
+	}
+
 	private static Function<String, Integer> function() {
 		return null;
 	}