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/3735#issuecomment-581522286,https://api.github.com/repos/pydata/xarray/issues/3735,581522286,MDEyOklzc3VlQ29tbWVudDU4MTUyMjI4Ng==,10194086,2020-02-03T17:20:31Z,2020-02-03T18:00:08Z,MEMBER,"I think the problem is in `_determine_cmap_params`:

https://github.com/pydata/xarray/blob/95e4f6c7a636878c94b892ee8d49866823d0748f/xarray/plot/utils.py#L262

This *may* have to be:
```python
if levels is not None:
```

Introducing this change does not break any test (`py.test xarray/tests/test_plot.py`) and runs your example successfully. However, it then causes the same problem as in #3744.

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