在NodeMS中使用Mongo的UpdateMany之后未处理的承诺拒绝

Question

我使用以下代码在mongo db中存储文档

const MongoClient = require('mongodb').MongoClient

MongoClient.connect(settings.DB_MONGO_CONNECTOR, (err, db) => {
    if (err) throw err
    this.mongoCollection = db.db(settings.DB_MONGO_TABLE)
        .collection(this.mongoTableName)
})

//......

let arr = []

//......

this.mongoCollection.updateMany(arr, (err) => {
    if (err) throw err
    console.log('Document was saved')
}, { upsert: true })

调用updateMany后我收到错误：

(node:8228) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): MongoError: The update operation document must contain at least one atomic operator.
(node:8228) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

为什么呢？它的有效命令与否？