remove direct import of nan
Is there a tag I can put into the PR to avoid having a full Travis run for tiny things like this?

 - [ ] closes #xxxx
 - [ ] tests added / passed
 - [ ] passes ``git diff upstream/master -u -- "*.py" | flake8 --diff``
 - [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=h1) Report
> Merging [#17185](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/929c66fd74da221078a67ea7fd3dbcbe21d642e0?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17185/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17185      +/-   ##
==========================================
- Coverage   90.99%   90.98%   -0.02%     
==========================================
  Files         162      162              
  Lines       49508    49507       -1     
==========================================
- Hits        45052    45042      -10     
- Misses       4456     4465       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <100%> (-0.01%)` | :arrow_down: |
| #single | `40.27% <0%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/sparse/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL2ZyYW1lLnB5) | `94.26% <100%> (-0.02%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.66% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=footer). Last update [929c66f...ee260b8](https://codecov.io/gh/pandas-dev/pandas/pull/17185?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @jbrockmendel : If you add `[ci skip]` to your commit, that will stop the builds.  However, even in cases like this, you should let the builds run just in case. thanks. pls try to phrase things more idiomaticallly. 'get rid of' is slang. @jreback dev workflow related thing: you don't need to merge locally to change the commit message, you can just do that with the github merge button i changed the actual commit message which u can't do from the screen > i changed the actual commit message which u can't do from the screen

Yes, you can (I use it all the time, at least I think). After the first click on 'squash and merge' you see a dialog to edit the commit message, no? > thanks. pls try to phrase things more idiomaticallly. 'get rid of' is slang.

Will do.  Thanks for helping me along the learning curve.