validateValue method
Validates the value.
Returns null
if the value is valid, otherwise an error message.
Call validate() instead of this method when using the validator.
Implementation
@override
String? validateValue(T? valueCandidate) {
if (log != null) {
debugPrint(log!(valueCandidate));
} else if (valueCandidate != null) {
debugPrint(valueCandidate.toString());
} else {
debugPrint(errorText);
}
return null;
}