public static function dateDiff($from, $to = null)
    {
        if (!$to) {
            $to = $from;
            $from = date("d/m/Y");
        }

        if (!$dateFrom = static::date("U", $from)) {
            return;
        }

        if (!$dateTo = static::date("U", $to)) {
            return;
        }

        $diff = $dateTo - $dateFrom;
        $days = round($diff / 86400);

        return $days;
    }