BUG: fixes unhandled NAType when plotting (#32073)
- [x] closes #32073
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

I'm still getting familiar with testing in python, so I'm struggling a bit with tests.
But it would be nice to have at least a test included. Any guidelines on it?
Looking forward for the review.