BUG: fixed fillna('') on a Int64 column causes TypeError: <U3 cannot b…
…e converted to an IntegerDtype(#44289)

- [x] closes #44289
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

this contribution is for a class project and need not be accepted but feedback is always appreciated
@aditzkabitz  can you merge master and address comments This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in main, address the comments and we can reopen.