BUG: invalid rolling window on empty input
State: closed

Added a raise Value Error for the case when window==0, Kindly refer to issue #21286 for the same

- [x] closes #21286 
- [x] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] A simple except cases added


Labels:
name: Reshaping
description: Concat, Merge/Join, Stack/Unstack, Explode

Comments:
Hello @uds5501! Thanks for updating the PR.





Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on June 08, 2018 at 14:07 Hours UTC
Respected Seniors, this is literally my first PR. Kindly do guide me if I do anything wrong here
Thanks for the PR! This appears to have broken a few tests. Be sure to check out the contributing to pandas guide and follow the steps locally to make sure you don't get any test errors before pushing to GitHub:

https://pandas.pydata.org/pandas-docs/stable/contributing.html


Some of those tests were added explicitly to test this in https://github.com/pandas-dev/pandas/pull/13441 (it was a PR to disallow negative windows, but explicitly tested windows of zero not too raise *upon construction*). 
I am not fully sure why those were added, so I think you can actually change those tests.
@uds5501 also general feedback: can you give the PR a more informative title? (you can still edit the title, see 'edit' button at the right of it)
@jorisvandenbossche I would do that soon and thanks for the link

Can you add a test to ensure that this raises? Also will eventually want a whatsnew note (probably 0.24 at this point)
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21291?src=pr&el=h1) Report
> Merging [#21291](https://codecov.io/gh/pandas-dev/pandas/pull/21291?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4274b840e64374a39a0285c2174968588753ec35?src=pr&el=desc) will **increase** coverage by `0.03%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21291/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/21291?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21291      +/-   ##
==========================================
+ Coverage   91.85%   91.89%   +0.03%     
==========================================
  Files         153      153              
  Lines       49546    49579      +33     
==========================================
+ Hits        45509    45559      +50     
+ Misses       4037     4020      -17
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.29% <100%> (+0.04%)` | :arrow_up: |
| #single | `41.85% <0%> (-0.02%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21291?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/window.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvd2luZG93LnB5) | `96.28% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/melt.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZWx0LnB5) | `97.34% <0%> (ø)` | :arrow_up: |
| [pandas/io/formats/csvs.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvY3N2cy5weQ==) | `98.14% <0%> (+0.01%)` | :arrow_up: |
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `93.16% <0%> (+0.02%)` | :arrow_up: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.8% <0%> (+0.02%)` | :arrow_up: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.17% <0%> (+0.05%)` | :arrow_up: |
| [pandas/core/reshape/pivot.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9waXZvdC5weQ==) | `97.03% <0%> (+0.05%)` | :arrow_up: |
| [pandas/io/formats/style.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvc3R5bGUucHk=) | `96.12% <0%> (+0.08%)` | :arrow_up: |
| [pandas/core/dtypes/missing.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL21pc3NpbmcucHk=) | `92.52% <0%> (+0.57%)` | :arrow_up: |
| [pandas/plotting/\_core.py](https://codecov.io/gh/pandas-dev/pandas/pull/21291/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb3JlLnB5) | `83.53% <0%> (+1.14%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21291?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/21291?src=pr&el=footer). Last update [4274b84...9f5745c](https://codecov.io/gh/pandas-dev/pandas/pull/21291?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

@WillAyd Please check the corrections now and see if it is good enough
@WillAyd were your comments addressed?
lgtm. @WillAyd 
thanks @uds5501  (and @WillAyd )