Return null (empty target object) if status code is 204 (#792)

jaxb/src/main/java/feign/jaxb/JAXBDecoder.java

@@ -66,7 +66,7 @@ public class JAXBDecoder implements Decoder {
 
   @Override
   public Object decode(Response response, Type type) throws IOException {
-    if (response.status() == 404)
+    if (response.status() == 404 || response.status() == 204)
       return Util.emptyValueOf(type);
     if (response.body() == null)
       return null;