Add missing space to the NotImplementedError's message for compound d…
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=h1) Report
> Merging [#17140](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f2b0bdc9bc4e57e101e306db7555eb7db28172e9?src=pr&el=desc) will **decrease** coverage by `0.04%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17140/graphs/tree.svg?token=eZ4WkYLtcO&width=650&src=pr&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17140      +/-   ##
==========================================
- Coverage   91.03%   90.98%   -0.05%     
==========================================
  Files         161      161              
  Lines       49405    49405              
==========================================
- Hits        44974    44950      -24     
- Misses       4431     4455      +24
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.77% <ø> (-0.02%)` | :arrow_down: |
| #single | `40.2% <ø> (-0.14%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.96% <ø> (-0.06%)` | :arrow_down: |
| [pandas/io/feather\_format.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2lvL2ZlYXRoZXJfZm9ybWF0LnB5) | `20% <0%> (-65.72%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.56% <0%> (-0.2%)` | :arrow_down: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.85% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.05% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17140?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/17140?src=pr&el=footer). Last update [f2b0bdc...868e9a0](https://codecov.io/gh/pandas-dev/pandas/pull/17140?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/17140?src=pr&el=h1) Report
> Merging [#17140](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f2b0bdc9bc4e57e101e306db7555eb7db28172e9?src=pr&el=desc) will **decrease** coverage by `0.04%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17140/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17140      +/-   ##
==========================================
- Coverage   91.03%   90.98%   -0.05%     
==========================================
  Files         161      161              
  Lines       49405    49405              
==========================================
- Hits        44974    44950      -24     
- Misses       4431     4455      +24
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.77% <ø> (-0.02%)` | :arrow_down: |
| #single | `40.2% <ø> (-0.14%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.96% <ø> (-0.06%)` | :arrow_down: |
| [pandas/io/feather\_format.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2lvL2ZlYXRoZXJfZm9ybWF0LnB5) | `20% <0%> (-65.72%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.56% <0%> (-0.2%)` | :arrow_down: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.85% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.05% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17140?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/17140?src=pr&el=footer). Last update [f2b0bdc...868e9a0](https://codecov.io/gh/pandas-dev/pandas/pull/17140?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @FKint : Don't worry about the test failures, #17142 is trying to address that.  When that's merged in, you should rebase this branch at that time. thanks!