map<U> method
No need valueConverter for Fail result. But for Success you should define it.
Implementation
ResultOf<U?> map<U>([U Function(T)? valueConverter]) {
if (isSuccess) {
if (valueConverter == null) {
throw Exception(
'If result is success then valueConverter should not be null',
);
}
return ResultOf.success<U>(valueConverter(value as T));
}
return fail(error);
}