How can I recreate previous behavior with nested path?

[CodeWithOz]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
Consider this nesting setup:

// nested.js
var NestedPropDef = {
  someProp: { type: String, default: '' },
};
var schema = new Schema(NestedPropDef, { minimize: false });
schema.statics = {
  getInstance() {
    var nestedObject = new NestedProp();
    nestedObject.someProp = 'something';
    console.log('[first log] value of nestedObject:', nestedObject);
    return nestedObject;
  },
});
var NestedProp = mongoose.model('NestedProp', schema);

exports.NestedPropDef = NestedPropDef;
exports.NestedProp = NestedProp;

// parent-file.js
var NestedPropDef = require('./nested').NestedPropDef;
var NestedProp = require('./nested').NestedProp;

var schema = new Schema({
  otherProp: { type: String, default: '' },
  nestedProp: NestedPropDef,
});

schema.methods.updateNestedProp = function (data, callback) {
  this.nestedProp = NestedProp.getInstance();
  console.log('[second log] value of nestedProp:', this.nestedProp);
  this.otherProp: data.otherProp;
  console.log('[third log] value of this:', this);
  this.save(callback);
});
var Parent = mongoose.model('Parent', schema);
module.exports = Parent;

The current behavior is this:

[first log] value of nestedObject: {
  someProp: 'something'
}
[second log] value of nestedProp: {}
[third log] value of this: {
  otherProp: 'some value'
  // nestedProp is missing
}

What is the expected behavior?
As of version 5.9.24, the log statements would be as follows:

[first log] value of nestedObject: {
  someProp: 'something'
}
[second log] value of nestedProp: {
  someProp: 'something'
}
[third log] value of this: {
  otherProp: 'some value',
  nestedProp: {
    someProp: 'something'
  }
}

I understand that using the schema of NestedProp would mostly restore the previous functionality, like this:

// nested.js
...
exports.NestedPropSchema = schema;
exports.NestedProp = NestedProp;

// parent-file.js
var NestedPropSchema = require('./nested').NestedPropSchema;
var NestedProp = require('./nested').NestedProp;

var schema = new Schema({
  otherProp: { type: String, default: '' },
  nestedProp: NestedPropSchema,
});
...

But this adds the _id field to nestedProp, which wasn't there previously. So the third log would be this:

[third log] value of this: {
  otherProp: 'some value',
  nestedProp: {
    someProp: 'something',
    _id: ...
  }
}

Maybe that's a tiny and worthy sacrifice, and I know there's a way to disable the automatic addition of the _id, but my objective is to restore the previous functionality so other subtle bugs don't creep up on me. How can I restore the results I was seeing in 5.9.24? Or was I always nesting incorrectly (and Mongoose was just working with my incorrect nesting)?

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

• Node: 10 and 12
• Mongoose: 5.10.3

[vkarpov15]

This is a bug in Mongoose, an unintended consequence of our fix for #9293 in v5.9.28. The fix will be in 5.10.4, sorry for the confusion!

[CodeWithOz]

@vkarpov15 awesome thanks! Looking forward to 5.10.4.