eslint-plugin: do not allow undefined as a value

[layershifter]

ESLint plugin should prevent passing undefined to properties:

makeStyles({
  // ❌ should throw
  root: { color: undefined },
  // ✅ should pass
  root: { color: 'red' }
})

[NotWoods]

This rule should also disallow empty strings

makeStyles({
  // ❌ should throw
  root: { color: '' }
})

[layershifter]

Agree, however [content](https://developer.mozilla.org/en-US/docs/Web/CSS/content) should have a special handling in errors:

makeStyles({
  // ❌ should throw and recommend to do `content: '""'`
  root: { ":before" { content: '' } },
  // ✅ all good
  root: { ":before" { content: '""' } }
})