final protected function getWithSeparator($key)
    {
        $structure = $this;
        $splitKeys = explode($this->separator, $key);
        foreach ($splitKeys as $key) {
            if (!isset($structure[$key])) {
                return null;
            }
            if (!is_array($structure[$key])) {
                return $structure[$key];
            }
            $structure = $structure[$key];
        }
        return $structure;
    }