def send_empty(self, message):
        """
        Eventually remove from the observer list in case of a RST message.

        :type message: Message
        :param message: the message
        :return: the message unmodified
        """
        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