public function setMonthBitmask($monthBitmask)
    {
        $monthBitmask = (int) $monthBitmask;

        if ($this->monthBitmask < 0) {
            throw new \UnderflowException('Value of "monthBitmask" must be greater than 0');
        }


        if ($this->exists() && $this->monthBitmask !== $monthBitmask) {
            $this->updated['monthBitmask'] = true;
        }

        $this->monthBitmask = $monthBitmask;

        return $this;
    }