公众号生成临时二维码，回调参数EventKey没有值？

【请求地址】: https://api.weixin.qq.com/cgi-bin/qrcode/create?access_token=38_E1tuvxvJvLtUiNL7xSbFtH1dAhoEquWeN0lS82W7q5JBYz3trOZlD3Zbw_x_6yigzvKsBhFAvjPZkE1R1m7G46F1FNZlqt-rlBRqnvIvIlp8MKyUIETRdyn3L9jAJWxHGxIIrHUYv_6XOw0bTQEcAEDEBP

【请求参数】：{"action_name":"QR_STR_SCENE","expire_seconds":10800,"action_info":{"scene":{"scene_str":"gift_1298439407299280897"}}}

【响应数据】：{"ticket":"gQEw8TwAAAAAAAAAAS5odHRwOi8vd2VpeGluLnFxLmNvbS9xLzAyWkFTcmgyNDRkMjAxTEJ2dzF2Y1gAAgS1taBfAwQwKgAA","expire_seconds":10800,"url":"http:\/\/weixin.qq.com\/q\/02ZASrh244d201LBvw1vcX"}

回调参数如下：

{"allFieldsMap":{"CreateTime":"1604367805","EventKey":"","Event":"subscribe","ToUserName":"gh_23f2d6a925d5","FromUserName":"oBERCwMXSsoM612rWNOnPKok14Wk","MsgType":"event"},"createTime":"1604367805","event":"subscribe","eventKey":"","fromUser":"oBERCwMXSsoM612rWNOnPKok14Wk","hardWare":{},"msgType":"event","scanCodeInfo":{},"sendLocationInfo":{},"sendPicsInfo":{"picList":[]},"toUser":"gh_23f2d6a925d5"}