fixes the issue #22953
- [x] closes #22953 
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @vvyomjjain! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/series.py`](https://github.com/vvyomjjain/pandas/blob/926723aa4f78625bb56fa2e520be7882fb3b3d2d/pandas/core/series.py) !

 @pep8speaks This is for the issue that while combining two series, it returned nan even when you had a fill_value argument. That was the issue I guess. 
P.S. I am pretty new to this, I don't understand what PEP8 issue means. Thanks can you fix the PR title to match the issue There is already an existing PR #22971 working on this issue. Additionally, this is an issue to add documentation and not change any code.

Feel free to work on any additional issues in the meantime or this issue if PR #22971 stalls. @mroeschke thank you for the clarification. I'll have a look at PR #22971. 