GenericExceptionHandler can't report into TEXT/PLAIN responses

As seen in SLIDER-51, exceptions (like NotFound) can't be mapped into text/plain responses.

it may be that the Response.status(s).entity(exception).build() logic just doesn't work for plaintext, in which case the handler should detect an unsupported mime type and just return the error code with an empty body. That might be the best approach for other binaries too.

or: simply catch the marshalling exception and downgrade to an empty-body status code. This would be a more graceful fallback, as it would catch all marshalling issues and return the original error code to the user