Airship\Cabin\Bridge\Landing\Blog::flattenOld PHP Method

    protected function flattenOld(array $oldItems) : array
    {
        $items = [];
        foreach ($oldItems as $old) {
            if ($old['series']) {
                $items[] = 'series_' . $old['series'];
            } else {
                $items[] = 'blogpost_' . $old['post'];
            }
        }
        return $items;
    }