static public function overdueDays($dueDate)
    {
        $dateDiff = date_diff(is_object($dueDate) ? $dueDate : FlexiBeeRO::flexiDateToDateTime($dueDate),
            new \DateTime());
        if ($dateDiff->invert == 1) {
            $ddif = $dateDiff->days * -1;
        } else {
            $ddif = $dateDiff->days;
        }

        return $ddif;
    }