BUG: fillna maximum recursion depth exceeded in cmp (GH18159).
- [x] closes #18159
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=h1) Report
> Merging [#18385](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1647a724ae5c9038cdd3cf4ebbf2273d1b6ab109?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/18385/graphs/tree.svg?height=150&src=pr&token=eZ4WkYLtcO&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18385      +/-   ##
==========================================
- Coverage   91.36%   91.34%   -0.02%     
==========================================
  Files         164      164              
  Lines       49718    49718              
==========================================
- Hits        45426    45417       -9     
- Misses       4292     4301       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.14% <100%> (ø)` | :arrow_up: |
| #single | `39.61% <100%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `94.54% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=footer). Last update [1647a72...7380624](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=h1) Report
> Merging [#18385](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c3c04e266cbc5e176cc6ef4dc385cdd88fda0669?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18385/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18385      +/-   ##
==========================================
+ Coverage   91.58%   91.58%   +<.01%     
==========================================
  Files         153      153              
  Lines       51250    51250              
==========================================
+ Hits        46935    46938       +3     
+ Misses       4315     4312       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.44% <100%> (+0.02%)` | :arrow_up: |
| #single | `40.67% <100%> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/18385/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `94.44% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18385/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18385/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/18385/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.25% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=footer). Last update [c3c04e2...03b2f6b](https://codecov.io/gh/pandas-dev/pandas/pull/18385?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 can you rebase I've implemented changes you've requested. Hello @kchomski-reef! Thanks for updating the PR.

 - In the file [`pandas/core/internals.py`](https://github.com/pandas-dev/pandas/blob/03b2f6b1e7d121b7b34bb998914c684357c0f98c/pandas/core/internals.py), following are the PEP8 issues :

> [Line 1853:13](https://github.com/pandas-dev/pandas/blob/03b2f6b1e7d121b7b34bb998914c684357c0f98c/pandas/core/internals.py#L1853): [W503](https://duckduckgo.com/?q=pep8%20W503) line break before binary operator
> [Line 1905:13](https://github.com/pandas-dev/pandas/blob/03b2f6b1e7d121b7b34bb998914c684357c0f98c/pandas/core/internals.py#L1905): [W503](https://duckduckgo.com/?q=pep8%20W503) line break before binary operator





##### Comment last updated on December 08, 2017 at 16:57 Hours UTC Changes applied as requested. can you rebase and fixup checks green thanks @gkonefal-reef 