validate method
Return null if valid, otherwise a ValidationException.
Implementation
@override
ValidationException? validate(Object? value) {
if (value is! num) {
return ValidationException(this, value);
}
if (min != null) {
if (inclusive ? value < min! : value <= min!) {
return ValidationException(this, value);
}
}
if (max != null) {
if (inclusive ? value > max! : value >= max!) {
return ValidationException(this, value);
}
}
return null;
}