call abstract method

String? call(
  1. String attribute,
  2. String value
)

Validates a field value and returns an error message if validation fails, or null if it succeeds.

This method should be implemented in concrete validation rule classes to define the validation logic.

Parameters:

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

Returns: A validation error message if the validation fails, or null if the validation succeeds.

Implementation

String? call(String attribute, String value);