code: protected function buildData()
      {
          $bizContent = $this->getBizContent();
          $bizContent = ArrayUtil::paraFilter($bizContent);// 过滤掉空值，下面不用在检查是否为空
  
          $signData = [
              // 公共参数
              'app_id'        => $this->appId,
              'method'        => $this->method,
              'format'        => $this->format,
              'charset'       => $this->charset,
              'sign_type'     => $this->signType,
              'timestamp'     => $this->timestamp,
              'version'       => $this->version,
              'notify_url'    => $this->notifyUrl,
  
              // 业务参数
              'biz_content'   => json_encode($bizContent, JSON_UNESCAPED_UNICODE),
          ];
  
          // 电脑支付  wap支付添加额外参数
          if (in_array($this->method, ['alipay.trade.page.pay', 'alipay.trade.wap.pay'])) {
              $signData['return_url'] = $this->returnUrl;
          }
  
          // 移除数组中的空值
          $this->retData = ArrayUtil::paraFilter($signData);
      }
docs: 构建 支付 加密数据
  @author helei