BUG: pd.Series.replace does not preserve the original dtype
- [ ] closes #33484
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @kotamatsuoka! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-06-06 10:18:53 UTC Hi @kotamatsuoka - is this still active? Looks like there's some test failures and linting errors (from `black`), if you fix them up we'll take another look @kotamatsuoka closing as stale. please comment if you want to continue and the PR will be reopened.