【mlflow】TypeError: 'NoneType' object does not support item assignment

mlflowが突然動かなくなった...

以下がエラーの内容。

Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 1473, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 882, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 880, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 865, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)  # type: ignore[no-any-return]
  File "/usr/local/lib/python3.10/dist-packages/mlflow/server/handlers.py", line 508, in wrapper
    return func(*args, **kwargs)
  File "/usr/local/lib/python3.10/dist-packages/mlflow/server/handlers.py", line 549, in wrapper
    return func(*args, **kwargs)
  File "/usr/local/lib/python3.10/dist-packages/mlflow/server/handlers.py", line 1438, in _search_experiments
    experiment_entities = _get_tracking_store().search_experiments(
  File "/usr/local/lib/python3.10/dist-packages/mlflow/store/tracking/file_store.py", line 302, in search_experiments
    exp = self._get_experiment(exp_id, view_type)
  File "/usr/local/lib/python3.10/dist-packages/mlflow/store/tracking/file_store.py", line 396, in _get_experiment
    meta["tags"] = self.get_all_experiment_tags(experiment_id)
TypeError: 'NoneType' object does not support item assignment

解決策

mlruns/{experiment_id}/meta.yamlが空白のものが含まれているフォルダが原因だった。なぜ、こんな空のファイルが生成されたかわからないが、これを手動で除くことで解決できた。