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/4044#issuecomment-625530671,https://api.github.com/repos/pydata/xarray/issues/4044,625530671,MDEyOklzc3VlQ29tbWVudDYyNTUzMDY3MQ==,7441788,2020-05-07T22:33:46Z,2020-05-07T22:33:46Z,CONTRIBUTOR,"@TomNicholas , yes, thank you.","{""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,614149170
https://github.com/pydata/xarray/issues/4044#issuecomment-625523538,https://api.github.com/repos/pydata/xarray/issues/4044,625523538,MDEyOklzc3VlQ29tbWVudDYyNTUyMzUzOA==,35968931,2020-05-07T22:13:08Z,2020-05-07T22:13:08Z,MEMBER,"Hi @seth-p ,

Just to be sure I understand your question, are you asking why `concat_dim` doesn't default to `None` in `open_mfdataset`?

If so, that behaviour is there currently because it's being adapted from a previous, different behaviour, which requires a special placeholder value to give certain backwards-compatible behaviour by default.

But you raise a good point that in future, when `combine='nested'`, the default value of `concat_dim` should be `None`, so I've [pushed a commit](https://github.com/pydata/xarray/pull/3926/commits/c14f9d1ca9620bcb8790e87b0531730578466690) to #3926 to ensure it will, and you should see that behaviour in the next major release.
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,614149170