Polish contribution

See gh-34949

Author: sbrannen

spring-messaging/src/main/java/org/springframework/messaging/support/MessageHeaderAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.

spring-messaging/src/test/java/org/springframework/messaging/support/MessageBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -239,21 +239,22 @@ void buildMultipleMessages() {
 		assertThat(message3.getHeaders().get("foo")).isEqualTo("bar3");
 	}
 
-	@Test
-	void buildReplyChannelHeaderMessage() {
+	@Test  // gh-34949
+	void buildMessageWithReplyChannelHeader() {
 		MessageHeaderAccessor headerAccessor = new MessageHeaderAccessor();
 		MessageBuilder<?> messageBuilder = MessageBuilder.withPayload("payload").setHeaders(headerAccessor);
 
-		headerAccessor.setHeader("replyChannel", "foo");
+		headerAccessor.setHeader(MessageHeaders.REPLY_CHANNEL, "foo");
 		Message<?> message1 = messageBuilder.build();
+		assertThat(message1.getHeaders().get(MessageHeaders.REPLY_CHANNEL)).isEqualTo("foo");
 
 		headerAccessor.setHeader("hannel", 0);
 		Message<?> message2 = messageBuilder.build();
-
-		assertThat(message1.getHeaders().get("replyChannel")).isEqualTo("foo");
 		assertThat(message2.getHeaders().get("hannel")).isEqualTo(0);
 
-		assertThatIllegalArgumentException().isThrownBy(() -> headerAccessor.setHeader("replyChannel", 0));
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> headerAccessor.setHeader(MessageHeaders.REPLY_CHANNEL, 0))
+				.withMessage("'%s' header value must be a MessageChannel or String", MessageHeaders.REPLY_CHANNEL);
 	}
 
 }