Omnipay\Alipay\Requests\LegacyAppPurchaseRequest::getParamsToSign PHP Method

    private function getParamsToSign()
    {
        $params = $this->parameters->all();
        $params['service'] = $this->service;
        $params = array_filter($params, 'strlen');
        $params = array_map(function ($v) {
            return sprintf('"%s"', $v);
        }, $params);
        return $params;
    }