html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/3404#issuecomment-542444444,https://api.github.com/repos/pydata/xarray/issues/3404,542444444,MDEyOklzc3VlQ29tbWVudDU0MjQ0NDQ0NA==,2448579,2019-10-15T23:21:07Z,2019-10-15T23:21:07Z,MEMBER,"Another bug I introduced. 

https://github.com/pydata/xarray/blob/3f9069ba376afa35c0ca83b09a6126dd24cb8127/xarray/core/groupby.py#L323-L326

I think we replace `isnan` with `duck_array_ops.isnull`

can you send in a PR?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,507524966