Error using flaskbb db upgrade after installing plugin

[jdb235]

I'm trying to install and activate the polls plugin (https://github.com/micha030201/flaskbb-plugin-polls). I installed it using pip install flaskbb-plugin-vanity, which worked fine, but when I run flaskbb db upgrade I get the following error:

Traceback (most recent call last):
  File "/usr/local/bin/flaskbb", line 33, in <module>
    sys.exit(load_entry_point('FlaskBB', 'console_scripts', 'flaskbb')())
  File "/usr/lib/python3.9/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python3.9/site-packages/flask/cli.py", line 596, in main
    return super().main(*args, **kwargs)
  File "/usr/lib/python3.9/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python3.9/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python3.9/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python3.9/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/usr/lib/python3.9/site-packages/click/decorators.py", line 21, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/lib/python3.9/site-packages/flask/cli.py", line 440, in decorator
    return __ctx.invoke(f, *args, **kwargs)
  File "/usr/lib/python3.9/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/flask_migrate/cli.py", line 136, in upgrade
    _upgrade(directory, revision, sql, tag, x_arg)
  File "/usr/lib/python3/dist-packages/flask_migrate/__init__.py", line 96, in wrapped
    f(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/flask_migrate/__init__.py", line 269, in upgrade
    config = current_app.extensions['migrate'].migrate.get_config(directory,
KeyError: 'migrate'