GH-3697: DelegatingInvocableHandler.invoke() returning null

* Optimize a MessagingMessageListenerAdapter returning null from the DelegatingInvocableHandler.invoke()

Fixes: #3697 

Signed-off-by: ivamly <[email protected]>

**Auto-cherry-pick to `3.2.x`**

spring-kafka/src/main/java/org/springframework/kafka/listener/adapter/DelegatingInvocableHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 the original author or authors.
+ * Copyright 2016-2025 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.
@@ -55,6 +55,7 @@
  *
  * @author Gary Russell
  * @author Wang Zhiyang
+ * @author Ivan Malutin
  *
  */
 public class DelegatingInvocableHandler {
@@ -167,6 +168,7 @@ public boolean isAsyncReplies() {
 	 * @throws Exception raised if no suitable argument resolver can be found,
 	 * or the method raised an exception.
 	 */
+	@Nullable
 	public Object invoke(Message<?> message, Object... providedArgs) throws Exception { //NOSONAR
 		Class<?> payloadClass = message.getPayload().getClass();
 		InvocableHandlerMethod handler = getHandlerForPayload(payloadClass);
@@ -186,8 +188,13 @@ public Object invoke(Message<?> message, Object... providedArgs) throws Exceptio
 		else {
 			result = handler.invoke(message, providedArgs);
 		}
-		Expression replyTo = this.handlerSendTo.get(handler);
-		return new InvocationResult(result, replyTo, this.handlerReturnsMessage.get(handler));
+		if (result != null) {
+			Expression replyTo = this.handlerSendTo.get(handler);
+			return new InvocationResult(result, replyTo, this.handlerReturnsMessage.get(handler));
+		}
+		else {
+			return null;
+		}
 	}
 
 	/**