protected function getDefaultValueForSet($stringValue)
    {
        $stringValue = trim($stringValue);

        if (empty($stringValue)) {
            return null;
        }

        $values = [];
        foreach (explode(',', $stringValue) as $v) {
            $values[] = trim($v);
        }
        if (count($values) === 0) {
            return null;
        }
        return $values;
    }