Getting django error even after deleting mistake line
i've just reinstalled python from source and problem was gone!
i've been trying djano project that include channels & redis. recently i recreated venv and i get following even after deleting mistaken line. is there a way to clear cache in django project and runserver again? 
''' line 52, in message
    to = models.ForeignKey(to='user',on_delete='',related_name = 'to')
  File "/home//python-projects/DjangoChannels/.env/lib/python3.8/site-packages/django/db/models/fields/related.py", line 801, in init
    raise TypeError('on_delete must be callable.')
TypeError: on_delete must be callable.'''