public static function getInstance(Spreadsheet $spreadsheet = null)
    {
        if ($spreadsheet !== null) {
            $instance = $spreadsheet->getCalculationEngine();
            if (isset($instance)) {
                return $instance;
            }
        }

        if (!isset(self::$instance) || (self::$instance === null)) {
            self::$instance = new self();
        }

        return self::$instance;
    }