Suggestion

Forking from #6228 (review): this is a small internal change that shouldn't impact any users.

if you wanted to go one step further and clean up our now out-of-style typeof x === 'undefined' checks as part of this - that'd be gr8

https://cs.github.com/typescript-eslint/typescript-eslint?q=%2Ftypeof+.%2B%3F+%5B%21%3D%5D%3D%3D+%27undefined%27%2F