Devise\Support\Sortable\Link::bustUpField PHP Method

    protected function bustUpField($field)
    {
        $relationship = null;
        if (strpos($field, '.') > -1) {
            $optArr = explode('.', $field);
            $relationship = $optArr[0];
            $field = $optArr[1];
            return array($relationship, $field);
        }
        return array($relationship, $field);
    }