Backport PR #25069 on branch 0.24.x (REGR: rename_axis with None should remove axis name)
Backport PR #25069: REGR: rename_axis with None should remove axis name
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=h1) Report
> Merging [#25079](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=desc) into [0.24.x](https://codecov.io/gh/pandas-dev/pandas/commit/4f865c5cb505650cd55a23946fbb44ca9d577c55?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25079/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           0.24.x   #25079      +/-   ##
==========================================
- Coverage   92.37%   92.36%   -0.01%     
==========================================
  Files         166      166              
  Lines       52397    52398       +1     
==========================================
  Hits        48400    48400              
- Misses       3997     3998       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.79% <100%> (ø)` | :arrow_up: |
| #single | `42.88% <85.71%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/25079/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.63% <100%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25079/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `88.04% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25079?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/25079?src=pr&el=footer). Last update [4f865c5...07f4282](https://codecov.io/gh/pandas-dev/pandas/pull/25079?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/25079?src=pr&el=h1) Report
> Merging [#25079](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=desc) into [0.24.x](https://codecov.io/gh/pandas-dev/pandas/commit/4f865c5cb505650cd55a23946fbb44ca9d577c55?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25079/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           0.24.x   #25079      +/-   ##
==========================================
- Coverage   92.37%   92.36%   -0.01%     
==========================================
  Files         166      166              
  Lines       52397    52398       +1     
==========================================
  Hits        48400    48400              
- Misses       3997     3998       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.79% <100%> (ø)` | :arrow_up: |
| #single | `42.88% <85.71%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/25079/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.63% <100%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25079/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `88.04% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25079?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/25079?src=pr&el=footer). Last update [4f865c5...07f4282](https://codecov.io/gh/pandas-dev/pandas/pull/25079?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
