code: private void setNegotiatedContentType() {
          ConnegHandler.NegotiatedMediaType negotiatedMediaType = exchange.getAttachment(ConnegHandler.NEGOTIATED_MEDIA_TYPE);
          MediaType negotiated = negotiatedMediaType == null ? responseContentType : negotiatedMediaType.produces;
          setResponseMediaType(negotiated);
      }
docs: If client accepts anything, json will be used