公众号附件上传接口文档中没有提item字段，返回的json中有个item数组，这个是啥东西，怎么接
https://developers.weixin.qq.com/doc/offiaccount/Asset_Management/Adding_Permanent_Assets.html {"media_id":"_nNB32znf8t01wY0MSAh5NK8uBta3DMooEE20k76-HwcjTSHK1QxfEsvGMAeiL3-","url":"http:\/\/mmbiz.qpic.cn\/mmbiz_png\/9Skkrk1FV9bFtTd8fiaxw5lNH4z05XR0oQxTAAnGGmJLzcKgdx9p0Yy0dvZc3xP2xumPZC2ZiaE6sKn5fZ30rcXA\/0?wx_fmt=png","item":[]}
