Performs /join/$room_id

        Args:
            room_id_or_alias (str): The room ID or room alias to join.

def join_room(self, room_id_or_alias):
        """Performs /join/$room_id

        Args:
            room_id_or_alias (str): The room ID or room alias to join.
        """
        if not room_id_or_alias:
            raise MatrixError("No alias or room ID to join.")

        path = "/join/%s" % quote(room_id_or_alias)

        return self._send("POST", path)