protected static function normalizeArray(array $content)
    {
        foreach ($content as $key => $value) {
            if ($value instanceof \SimpleXMLElement) {
                if ($value->count()) {
                    $content[$key] = static::normalizeArray((array) $value);
                } else {
                    $content[$key] = null;
                }
            } elseif (is_array($value)) {
                $content[$key] = static::normalizeArray($value);
            }
        }

        return $content;
    }