Populate virtual with lean and transform cause null in array

[conduongtong]

Prerequisites

• I have written a descriptive issue title

Mongoose version

6.7.4

Node.js version

18.12.1

MongoDB version

6.0.2

Operating system

Windows

Operating system version (i.e. 20.04, 11.3, 10)

No response

Issue

I have an example like this:

const test = async () => {
  const parentSchema = new Schema({ title: String });
  const childSchema = new Schema({ title: String, parent: { type: mongoose.Schema.Types.ObjectId, ref: 'Parent' } });

  parentSchema.virtual('children', {
    ref: 'Child',
    localField: '_id',
    foreignField: 'parent',
  });
  const Parent = mongoose.model('Parent', parentSchema);

  const Child = mongoose.model('Child', childSchema);

  await Parent.create({ title: 'parent' });
  await Child.create({ title: 'child' });
  console.log(
    await Parent.find()
      .lean()
      .populate({
        path: 'children',
        match: { title: 'child' },
        select: '-__v',
        strictPopulate: false,
        transform: doc => {
          if (doc?._id) {
           // do something
            return doc;
          }
          return doc;
        },
      }),
  );
};

If I use .lean() with transform in populate, result will return [null] like this:

[
  {
    _id: new ObjectId("6386cc026dd86392014c9863"),
    title: 'parent',
    __v: 0,
    children: [null]
  }
]

Expect output:

children: []

Please help!