private function convertTimestampToDateTime($date)
    {
        if (false === ($date instanceof \DateTime) && false === is_int($date)) {
            throw new InvalidArgumentException(
                'Page::convertTimestampToDateTime() expect date argument to be an integer or an instance of \DateTime'
            );
        } elseif (is_int($date)) {
            $date = new \DateTime(date('c', $date));
        }

        return $date;
    }