protected function config(string $key)
    {
        $config = json_decode($this->header('config'), true);
        $definition = explode('.', $key);
        $item = isset($config[$definition[0]]) ? $config[$definition[0]] : null;

        $numberOfDefinitions = count($definition);

        for ($i = 1; $i < $numberOfDefinitions; ++$i) {
            $item = isset($item[$definition[$i]]) ? $item[$definition[$i]] : null;
        }

        return $item;
    }