parseValue method
Parse one value: check missing values, the type, then the rules.
Implementation
@override
Object? parseValue(Object? input, ParseState state, List<Object> path) {
if (input is Undefined) {
return undefined;
}
int before = state.issues.length;
Object? output = inner.parseValue(input, state, path);
return runRules(output, before, state, path);
}