code: protected void handleExceptions(MessageEvent messageEvent, Exception exception) {
          logger.error("Unknown exception. Internal Server Error.", exception);
          writeErrorResponse(messageEvent,
                             HttpResponseStatus.INTERNAL_SERVER_ERROR,
                             "Internal Server Error");
      }
docs: Exceptions specific to each operation is handled in the corresponding
  subclass. At this point we don't know the reason behind this exception.
  
  @param exception