call method

@override String? call(String attribute, String value)

Validates whether a value is entirely in uppercase.

This method checks if the input value consists of uppercase letters only. If the value contains any lowercase letters or is empty, an error message is generated using the buildMessage method.

Parameters:

• attribute: The identifier of the form attribute being validated.
• value: The value to be validated.

Returns: A validation error message if the value is not entirely in uppercase or is empty, or null if the value is in uppercase.

Implementation

@override
String? call(String attribute, String value) {
  if (value.isNotEmpty) {
    if (value.toUpperCase() != value) {
      return buildMessage(attribute, value);
    }
  }
  return null;
}