chore(null): yarn null:autoadd

[dbjorge]

Description of changes

This is just the result of running yarn null:autoadd to add strict null checking for the files that already support it

Pull request checklist

• Addresses an existing issue: part of Codebase should use strict null checks #2869
• Ran yarn fastpass
• [n/a] Added/updated relevant unit test(s) (and ran yarn test)
• [n/a] Verified code coverage for the changes made. Check coverage report at: <rootDir>/test-results/unit/coverage
• PR title AND final merge commit title both start with a semantic tag (fix:, chore:, feat(feature-name):, refactor:). See CONTRIBUTING.md.
• [n/a] (UI changes only) Added screenshots/GIFs to description above
• [n/a] (UI changes only) Verified usability with NVDA/JAWS

[dbjorge]

Subsuming this into a later PR with corrections to the autoadd behavior