Dont check for NaTType, just NaT
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

lgtm. merge on green. Test error is in `pyarrow`, which I haven't looked at closely.  Does it instantiate a new instance of `NaTType` for some reason? no just rebase # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=h1) Report
> Merging [#17564](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3795272ad8987f5af22c5887fc95bb35c1b6bb69?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/17564/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17564      +/-   ##
==========================================
- Coverage   91.19%   91.17%   -0.02%     
==========================================
  Files         163      163              
  Lines       49626    49625       -1     
==========================================
- Hits        45258    45248      -10     
- Misses       4368     4377       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.96% <100%> (-0.01%)` | :arrow_down: |
| #single | `40.19% <0%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.19% <100%> (ø)` | :arrow_up: |
| [pandas/io/packers.py](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhY2tlcnMucHk=) | `88.19% <100%> (-0.04%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.77% <0%> (-0.1%)` | :arrow_down: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=footer). Last update [3795272...663ba90](https://codecov.io/gh/pandas-dev/pandas/pull/17564?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!