Error about load_metric
{'login': 'jiacheng-ye', 'id': 30772464, 'node_id': 'MDQ6VXNlcjMwNzcyNDY0', 'avatar_url': 'https://avatars.githubusercontent.com/u/30772464?v=4', 'gravatar_id': '', 'url': 'https://api.github.com/users/jiacheng-ye', 'html_url': 'https://github.com/jiacheng-ye', 'followers_url': 'https://api.github.com/users/jiacheng-ye/followers', 'following_url': 'https://api.github.com/users/jiacheng-ye/following{/other_user}', 'gists_url': 'https://api.github.com/users/jiacheng-ye/gists{/gist_id}', 'starred_url': 'https://api.github.com/users/jiacheng-ye/starred{/owner}{/repo}', 'subscriptions_url': 'https://api.github.com/users/jiacheng-ye/subscriptions', 'organizations_url': 'https://api.github.com/users/jiacheng-ye/orgs', 'repos_url': 'https://api.github.com/users/jiacheng-ye/repos', 'events_url': 'https://api.github.com/users/jiacheng-ye/events{/privacy}', 'received_events_url': 'https://api.github.com/users/jiacheng-ye/received_events', 'type': 'User', 'site_admin': False}
[{'id': 1935892857, 'node_id': 'MDU6TGFiZWwxOTM1ODkyODU3', 'url': 'https://api.github.com/repos/huggingface/datasets/labels/bug', 'name': 'bug', 'color': 'd73a4a', 'default': True, 'description': "Something isn't working"}]
[]
Hi ! I wasn't able to reproduce your error.

Can you try to clear your cache at `~/.cache/huggingface/modules` and try again ?
## Describe the bug
  File "/opt/conda/lib/python3.8/site-packages/datasets/load.py", line 1371, in load_metric
    metric = metric_cls(
TypeError: 'NoneType' object is not callable

## Steps to reproduce the bug
```python
metric = load_metric("glue", "sst2")
```


## Environment info
- `datasets` version: 1.16.1
- Platform: Linux-4.15.0-161-generic-x86_64-with-glibc2.10
- Python version: 3.8.3
- PyArrow version: 6.0.1

{'url': 'https://api.github.com/repos/huggingface/datasets/issues/3422/reactions', 'total_count': 0, '+1': 0, '-1': 0, 'laugh': 0, 'hooray': 0, 'confused': 0, 'heart': 0, 'rocket': 0, 'eyes': 0}