Ошибка KeyError: '13888480557292346'

Написал мидовар, но при запуске если передать несколько фотографий то выдаёт ошибку:

    total_after = len(self.album[event.media_group_id]['messages'])
                      ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
KeyError: '13888480557292346'

class AlbumMiddleware(BaseMiddleware):
    def __init__(
            self,
            latency: Union[int, float] = 0.1
    ) -> None:
        self.latency = latency
        self.album = {}

    def collect_album_message(self, event: Message):
        if event.media_group_id not in self.album:
            self.album[event.media_group_id] = {'messages': []}
            self.album[event.media_group_id]['messages'].append(event)

            return len(self.album[event.media_group_id]['messages'])

    async def __call__(
        self,
        handler: Callable[[Message, Dict[str, Any]], Awaitable[Any]],
        event: Message,
        data: Dict[str, Any]
    ) -> Any:
        if not event.media_group_id:
            return await handler(event, data)

        total_before = self.collect_album_message(event)
        await asyncio.sleep(self.latency)
        total_after = len(self.album[event.media_group_id]['messages'])

        if total_before != total_after:
            return

        album_messages = self.album[event.media_group_id]['messages']
        album_messages.sort(key=lambda x: x.message_id)
        data['album'] = album_messages

        await handler(event, data)

        del self.album[event.media_group_id]