onValidate method

@override String? onValidate(String entityName, T? value)

Returns the validation message by the child class extending Rule.

Override it in the child class to define the validation logic for it.

Implementation

@override
String? onValidate(String entityName, T? value) {
  if (value == null ||
      isEmptyIterable(value) ||
      isEmptyMap(value) ||
      isEmptyString(value)) {
    return ':entity is required.';
  }
  return null;
}