Date Objects not copied to new document when using Model Constructors & Strict: False Schema

[SamuelMaddox]

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

Current behavior
Properties on objects that contain a value of type Date are not persisted to a document when passing an object into a model constructor, where the model is based off of a schema with the strict: false option set. This previously worked in version 5.5.1

Steps to reproduce.

const mongoose = require('mongoose');

// === Connect to MongoDB ===
const mongoURI = 'mongodb://localhost:27017';
const mongoOpts = {
  dbName: 'mongooseBug',
  useNewUrlParser: true,
  useCreateIndex: true,
}
mongoose.connect(mongoURI, mongoOpts);

// === Create Schema/Model
const schema = mongoose.Schema({}, { strict: false });
const SettingsModel = mongoose.model('Settings', schema);

// === Create Document ===
const settingsObject = {
  timestamp: new Date(),
  subDoc: {
    timestamp: new Date(),
  },
}
const settingsDocument = new SettingsModel(settingsObject);

// === Output Actual & Expected Documents
console.log('=== ACTUAL DOCUMENT ===')
console.log(settingsDocument);

console.log('\n=== EXPECTED DOCUMENT ===')
console.log({
  _id: '<AUTO GENERATED>',
  timestamp: settingsObject.timestamp,
  subDoc: {
    timestamp: settingsObject.subDoc.timestamp
  },
});

// === Save Document & Close MongoDB Connection ===
settingsDocument.save((err) => {
  mongoose.connection.close()
});

What is the expected behavior?
I expect the following to be logged out & saved to DB:

=== EXPECTED DOCUMENT ===
{ _id: '<AUTO GENERATED>',
  timestamp: 2019-06-17T23:02:07.711Z,
  subDoc: { timestamp: 2019-06-17T23:02:07.711Z } }

Instead I get the following:

=== ACTUAL DOCUMENT ===
{ _id: 5d081cb010dcaa21488d97d2 }

What are the versions of Node.js, Mongoose and MongoDB you are using?
Node: 10.7.0
Mongoose: 5.5.2 - 5.6.0. Version 5.5.1 provides the expected output
MongoDB: 4.0 & 3.6

[vkarpov15]

Thanks for reporting this issue, we put a fix into master and it will be released with v5.6.1 next week.