call method

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

Validates whether a value contains only lowercase characters.

This method checks if the input value consists of lowercase letters only by comparing it with a lowercase version of itself. If the value contains any uppercase letters or other characters, 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 contains non-lowercase characters, or null if the value is valid.

Implementation

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