public function validateSpecific(array $required = [])
    {
        foreach ($required as $field) {
            /*
             * If the field is in the required array, and the
             * object attribute equals null, we'll throw an exception.
             */
            if (in_array($field, $this->required) && $this->getAttribute($field) === null) {
                throw new AdldapException(sprintf($this->messages['required'], $field));
            }
        }

        return true;
    }