isUpperCase method Null safety

Validator isUpperCase(
  1. {String message = "Validator.isUpperCase"}
)

Returns a Validator that accepts a value where all letters are upper-case.

TODO: Check whether there is a better way to validate this.

Implementation

Validator isUpperCase({
  String message = "Validator.isUpperCase",
}) {
  return add(
    (value) => value == value?.toUpperCase() ? null : message,
  );
}