云函数代码如下: const cloud = require('wx-server-sdk') cloud.init({  env: 'egyptmanagement-8a2de' }) const db = cloud.database() const _ = db.command const $ = db.command.aggregate // 云函数入口函数 exports.main = async(event, context) => {  //var cmd = event.cmd;  console.log(event);  db.collection('eat').aggregate().group({    _id: {      address: '$address',      date: '$date',      type: '$type'    },    tsum: $.sum('$number')  }).end().then(res => {    console.log("结果:",res)    return res  })  return null } eat collection里面有5条数据. number是整形,非字符串 调用查看日志成功, 但是确始终没有数据返回,