Swimbot Error

Traceback (most recent call last):
  File "/home/pi/.local/lib/python3.7/site-packages/discord/ext/commands/core.py", line 85, in wrapped
    ret = await coro(*args, **kwargs)
  File "/home/pi/Swimbot/premium.py", line 144, in allowed
    if '#' not in tag: tag = f'#{tag}'
TypeError: argument of type 'NoneType' is not iterable