private function convertRecursive(array $array, $parentKey = null)
    {
        $return = [];
        if (!is_null($parentKey))
            $parentKey .= '.';

        foreach ($array as $k => $v) {
            if (is_array($v))
                $return[] = $this->convertRecursive($v, $parentKey . $k);
            else
                $return[$parentKey . $k] = $v;
        }
        return $this->array_flatten($return);
    }