code: def send_empty(self, message):
          
          host, port = message.destination
          key_token = hash(str(host) + str(port) + str(message.token))
          if key_token in self._relations and message.type == defines.Types["RST"]:
              del self._relations[key_token]
          return message
docs: Eventually remove from the observer list in case of a RST message.
  
          :type message: Message
          :param message: the message
          :return: the message unmodified