code: def callback(self, herald_svc, message):
          
          if self.__callback is not None:
              try:
                  # pylint: disable=W0703
                  self.__callback(herald_svc, message)
              except Exception as ex:
                  _logger.exception("Error calling callback: %s", ex)
docs: Tries to call the callback of the post message.
          Avoids errors to go outside this method.
  
          :param herald_svc: Herald service instance
          :param message: Received answer message