Merge pull request #32622 from NadChel:bugfix/GH-32620_remove_content_type_if_no_body

* gh-32622:
  Polishing external contribution
  Remove Content-Type when body is empty

spring-web/src/main/java/org/springframework/http/codec/EncoderHttpMessageWriter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -127,6 +127,7 @@ public class EncoderHttpMessageWriter<T> implements HttpMessageWriter<T> {
 			return body
 					.singleOrEmpty()
 					.switchIfEmpty(Mono.defer(() -> {
+						message.getHeaders().setContentType(null);
 						message.getHeaders().setContentLength(0);
 						return message.setComplete().then(Mono.empty());
 					}))

spring-web/src/test/java/org/springframework/http/codec/EncoderHttpMessageWriterTests.java

@@ -33,7 +33,9 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
+import org.springframework.core.ResolvableType;
 import org.springframework.core.codec.CharSequenceEncoder;
+import org.springframework.core.codec.Encoder;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.http.MediaType;
@@ -199,6 +201,30 @@ class EncoderHttpMessageWriterTests {
 		assertThat((Boolean) method.invoke(writer, TEXT_HTML)).isFalse();
 	}
 
+	@Test
+	public void noContentTypeWithEmptyBody() {
+		Encoder<CharSequence> encoder = CharSequenceEncoder.textPlainOnly();
+		HttpMessageWriter<CharSequence> writer = new EncoderHttpMessageWriter<>(encoder);
+		Mono<Void> writerMono = writer.write(Mono.empty(), ResolvableType.forClass(String.class),
+				null, this.response, NO_HINTS);
+
+		StepVerifier.create(writerMono)
+				.verifyComplete();
+		assertThat(response.getHeaders().getContentType()).isNull();
+	}
+
+	@Test
+	public void zeroContentLengthWithEmptyBody() {
+		Encoder<CharSequence> encoder = CharSequenceEncoder.textPlainOnly();
+		HttpMessageWriter<CharSequence> writer = new EncoderHttpMessageWriter<>(encoder);
+		Mono<Void> writerMono = writer.write(Mono.empty(), ResolvableType.forClass(String.class),
+				null, this.response, NO_HINTS);
+
+		StepVerifier.create(writerMono)
+				.verifyComplete();
+		assertThat(this.response.getHeaders().getContentLength()).isEqualTo(0);
+	}
+
 	private void configureEncoder(MimeType... mimeTypes) {
 		configureEncoder(Flux.empty(), mimeTypes);
 	}