CLN: Switch to using `is not None` rather than `bool()`
- [x] closes #32720
- [ ] tests added / passed - This change seemed trivial to *add* tests and should be covered by existing ones. 
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [] whatsnew entry
