/**
  * {@inheritDoc}
  */
 public function isRequiredExistingClass($className, $suppressException = true)
 {
     /* Clear the last error. */
     $this->lastError = null;
     /* If valid just return true. */
     if (Validator::isRequiredExistingClass($className)) {
         return true;
     }
     /* Set the error message. */
     $this->lastError = sprintf('Expected class name, \'%s\' given.', $className);
     return $this->validationFailed($suppressException);
 }