Uses a geventified Room subclass

def _mkroom(self, room_id: str) -> Room:
        """ Uses a geventified Room subclass """
        if room_id not in self.rooms:
            self.rooms[room_id] = Room(self, room_id)
        room = self.rooms[room_id]
        if not room.canonical_alias:
            room.update_aliases()
        return room