<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def start(self):
 """ Initiate the session by starting to execute the command with the peer. :return: The :attr:`~.xso.Command.first_payload` of the response This sends an empty command IQ request with the :attr:`~.ActionType.EXECUTE` action. The :attr:`status`, :attr:`response` and related attributes get updated with the newly received values. """


        if self._response is not None:
            raise RuntimeError("command execution already started")

        request = aioxmpp.IQ(
            type_=aioxmpp.IQType.SET,
            to=self._peer_jid,
            payload=adhoc_xso.Command(self._command_name),
        )

        self._response = yield from self._stream.send_iq_and_wait_for_reply(
            request,
        )

        return self._response.first_payload