message: fix(core): compare with undefined instead of 'undefined'
diff: @@ -30,7 +30,6 @@ export function isDocumentIdentifier(
  state: unknown
  ): state is DocumentIdentifier {
  return (
  - state !== 'undefined' &&
  - (state as DocumentIdentifier).$$typeof !== undefined
  + state !== undefined && (state as DocumentIdentifier).$$typeof !== undefined
  )
  }
  