/**
     * Get Product_code min
     *
     * @return integer
     */
    public function getCodeMin()
    {
        $this->_calc();

        $codes = array();
        foreach ($this->codes as $code) {
            if (!is_null($code)) {
                $codes[] = $code;
            }
        }
        return count($codes) ? min($codes) : null;
    }