Fix incorrect Content-Type for POST/PUT/PATCH requests without body

Signed-off-by: banseok1216 <bansuk1216@naver.com>

See gh-1018

Author: banseok1216

spring-restdocs-core/src/main/java/org/springframework/restdocs/http/HttpRequestSnippet.java

@@ -175,7 +175,7 @@ private void writeMultipartEnd(PrintWriter writer) {
 
 	private boolean requiresFormEncodingContentTypeHeader(OperationRequest request) {
 		return request.getHeaders().get(HttpHeaders.CONTENT_TYPE) == null && isPutPostOrPatch(request)
-				&& !includeParametersInUri(request);
+				&& request.getContent().length > 0 && !includeParametersInUri(request);
 	}
 
 	private Map<String, String> header(String name, String value) {

spring-restdocs-core/src/test/java/org/springframework/restdocs/http/HttpRequestSnippetTests.java

@@ -138,6 +138,13 @@ public void postRequestWithCharset() throws IOException {
 				.content(japaneseContent));
 	}
 
+	@Test
+	public void postRequestWithNoContentTypeAndNoBodyDoesNotIncludeContentTypeHeader() throws IOException {
+		new HttpRequestSnippet().document(this.operationBuilder.request("http://localhost/foo").method("POST").build());
+		assertThat(this.generatedSnippets.httpRequest())
+			.is(httpRequest(RequestMethod.POST, "/foo").header(HttpHeaders.HOST, "localhost"));
+	}
+
 	@Test
 	public void putRequestWithContent() throws IOException {
 		String content = "Hello, world";