findByIdAndUpdate + .select returns only _id on v >= 6.9.3, < 7.0.0

[draperunner]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

6.9.3

Node.js version

16

MongoDB server version

4.4

Typescript version (if applicable)

No response

Description

After upgrading to the latest version of mongoose v6.x, I noticed that only the _id field was returned from one of my update statements, resulting in errors trying to access data on undefined subdocuments.

In my case, I am using select("+optionalfield"), but it seems any projection fails.

const updated = await Kitten.findByIdAndUpdate(silence._id, { age: 3 })
  .select("+age")

console.log("UPDATED", updated) // <-- Returns _id only, not name or age!

Result:

{ _id: new ObjectId("644c3025179705584f9945aa") }

Expected result:

{
  _id: new ObjectId("644c3025179705584f9945aa"),
  name: 'Silence',
  age: 2,
  __v: 0
}

I have reproduced this on different versions of mongoose and it seems that v6.9.3 introduced this error.

Upgrading to v7 has fixed it for me, but I guess you might want to release a fix on v6.

Steps to Reproduce

Install mongoose version 6.x and run the following code:

const mongoose = require('mongoose');

async function main() {
  await mongoose.connect('mongodb://127.0.0.1:27017/test');

  const kittySchema = new mongoose.Schema({
      name: String,
      age: {
        select: false,
        type: Number
      }
    });

  const Kitten = mongoose.model('Kitten', kittySchema);
  const silence = new Kitten({ name: 'Silence', age: 2 });
  await silence.save()

  const updated = await Kitten.findByIdAndUpdate(silence._id, { age: 3 })
    .select("+age")

  console.log("UPDATED", updated) // <-- Returns _id only, not name or age!
}

main()

Expected Behavior

The following code

const updated = await Kitten.findByIdAndUpdate(silence._id, { age: 3 })
  .select("+age")

console.log(updated)

should return:

{
  _id: new ObjectId("644c3025179705584f9945aa"),
  name: 'Silence',
  age: 2,
  __v: 0
}

but instead returns:

{ _id: new ObjectId("644c3025179705584f9945aa") }