Minor Description
There's an issue with the wrong informational message being displayed if the response entity is empty (so only status code).
Also, I believe when populating the response entity type (and given a Response object), the wrong type is used to filter the set of possible types (i.e. Response.class is used instead of Response.getEntity()). This doesn't really change anything since the possible response media type set will be the same in the end for the vast majority of cases since most MessageBodyWriter/Readers use Object as the generic type and you would have to use a specific generic type.