Return 500 if producible attribute present

When a request is mapped through a producible condition on an
@RequestMapping, then a failure to find a converter/decoder should be
a 500 because the return type + media type pair were declared by the
controller and that should be possible to render.

Closes gh-23287

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -309,7 +309,11 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 		}
 
 		if (body != null) {
-			if (isContentTypePreset) {
+			Set<MediaType> producibleMediaTypes =
+					(Set<MediaType>) inputMessage.getServletRequest()
+							.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
+
+			if (isContentTypePreset || !CollectionUtils.isEmpty(producibleMediaTypes)) {
 				throw new HttpMessageNotWritableException(
 						"No converter for [" + valueType + "] with preset Content-Type '" + contentType + "'");
 			}