Merge branch '5.2.x'

spring-messaging/src/main/java/org/springframework/messaging/core/MessagePostProcessor.java

@@ -28,13 +28,14 @@ import org.springframework.messaging.Message;
  * @see MessageSendingOperations
  * @see MessageRequestReplyOperations
  */
+@FunctionalInterface
 public interface MessagePostProcessor {
 
 	/**
 	 * Process the given message.
 	 * @param message the message to process
-	 * @return a post-processed variant of the message,
-	 * or simply the incoming message; never {@code null}
+	 * @return a post-processed variant of the message, or simply the incoming
+	 * message; never {@code null}
 	 */
 	Message<?> postProcessMessage(Message<?> message);