class BlankValidator

BlankValidatorTest.php in drupal/core/vendor/symfony/validator/Symfony/Component/Validator/Tests/Constraints/BlankValidatorTest.php

class BlankValidator extends ConstraintValidator {

  /**
   * {@inheritDoc}
   */
  public function validate($value, Constraint $constraint) {
    if ('' !== $value && null !== $value) {
      $this->context
        ->addViolation($constraint->message, array(
        '{{ value }}' => $value,
      ));
    }
  }

}