BUG - Subdocument mapping that has select: false results in MongoDB Server Error

[Refzlund]

Bug Report

Before creating an issue please make sure you are using the latest version of mongoose
Getting a Operaion ... timed out after 10000ms error? Read this FAQ entry: https://mongoosejs.com/docs/faq.html#operation-buffering-timed-out
Getting a x.$__y is not a function error? Read this FAQ entry: https://mongoosejs.com/docs/faq.html#not-a-function

What is the current behavior?

When a document maps a subdocument — Map({ field: 'hello', number: 0 }, { field: 'world', number: 1 } )

The subdocument contains a property with select: false for ex. number — Map({ field: 'hello' }, { field: 'world' } )

Mongoose will query:

document.findOne { _id: new ObjectId("623ec001e3d4002a123561e7") } {
  projection: {
    'subdocuments.$*.number': 0
  }
}

Resulting in a MongoDB error response:
FieldPath field names may not start with '$'. Consider using $getField or $setField.

Steps to reproduce

const subdocument = new Schema({
	selected: { type: Number }, 
	not_selected: { type: Number, select: false }
})

const document = new Schema({
	subdocument_mapping: {
		type: Map,
		of: subdocument
	}
})

const Document = mongoose.model('User', document)
mongoose.set('debug', true)
mongoose.set('debug', function (coll, method, query, doc) {
	console.log(`${coll}.${method}`, query, doc)
})

async function test() {
	await Document.find({})
}

Console log

users.find {} { projection: { 'subdocument_mapping.$*.not_selected': 0 } }
FieldPath field names may not start with '$'. Consider using $getField or $setField.
MongoServerError: FieldPath field names may not start with '$'. Consider using $getField or $setField.
    at Connection.onMessage (C:\Temp\Mongoose bug\node_modules\mongodb\lib\cmap\connection.js:203:30)
    at MessageStream.<anonymous> (C:\Temp\Mongoose bug\node_modules\mongodb\lib\cmap\connection.js:63:60)
    at MessageStream.emit (node:events:526:28)
    at processIncomingData (C:\Temp\Mongoose bug\node_modules\mongodb\lib\cmap\message_stream.js:108:16)
    at MessageStream._write (C:\Temp\Mongoose bug\node_modules\mongodb\lib\cmap\message_stream.js:28:9)
    at writeOrBuffer (node:internal/streams/writable:389:12)
    at _write (node:internal/streams/writable:330:10)
    at MessageStream.Writable.write (node:internal/streams/writable:334:10)
    at TLSSocket.ondata (node:internal/streams/readable:754:22)
    at TLSSocket.emit (node:events:526:28)

What is the expected behavior?

No errors are thrown, document is fetched with the subdocuments. The subdocument will query select: false, as expected, using the property.

What are the versions of Node.js, Mongoose and MongoDB you are using?

package.json
"mongoose": "^6.3.0"

Node.js
v16.14.2

[IslandRhythms]

const mongoose = require('mongoose');
const {Schema} = mongoose;

const subdocument = new Schema({
	selected: { type: Number }, 
	not_selected: { type: Number, select: false }
})

const document = new Schema({
	subdocument_mapping: {
		type: Map,
		of: subdocument
	}
})

const Document = mongoose.model('User', document)
mongoose.set('debug', true)
mongoose.set('debug', function (coll, method, query, doc) {
	console.log(`${coll}.${method}`, query, doc)
})

async function test() {
    await mongoose.connect('mongodb://localhost:27017');
    await mongoose.connection.dropDatabase();
	await Document.find({})
}

test();