[material-ui][Switch] Undefined/null values in the theme causes crash

[beaktor]

Steps to reproduce

https://github.com/mui/material-ui/pull/41367/files#r1586868393

I can put some effort in making an environment, but I hope the comment above is enough using code inspection to suffice for "steps to reproduce". Requested by @siriwatknp, suggested fix included in the PR comment above.

Current behavior

Themes with a undefined/null value will crash

Expected behavior

While not happy path, Switch should tolerate themes with a value that is undefined/null.

Context

Our application dynamically switches between themes, and some themes have extra definitions. These defs might appear as null when it's not relevant. This recent change chokes on that change.

Your environment

npx @mui/envinfo

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  Output from `npx @mui/envinfo` goes here.

Search keywords: switch theme undefined null crash

[mnajdova]

@siriwatknp a quick reminder to look into this.

[ZeeshanTamboli]

Fixed in #42147