read static method
Apple's appleValue read as a member: unknown for a value this version
does not name, null when Apple sent nothing. See ProcessingState.read,
which says why reading to a member first is what makes the branches
exhaustive.
Implementation
static ExternalBuildState? read(String? appleValue) => appleValue == null
? null
: values.firstWhere(
(s) => s.appleValue == appleValue,
orElse: () => unknown,
);