Passing undefined to mongoose's Model.create with vs without a callback

[OfirD1]

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

What is the current behavior?

I'm getting a different behavior when passing undefined to a mongoose's model's create when using vs. not using a callback.

steps to reproduce

An example:

const mongoose = require('mongoose');
const userSchema = new mongoose.Schema({ name: { type: String, default: null } });
const User = mongoose.model('User', userSchema);
const user = undefined;

// compare this
User.create(user).then(createdUser => console.log(createdUser.name)); 

// with this
User.create(user, (err, createdUser) => console.log(createdUser.name)); 

In the first case, no User record is created in the database, and createdUser is undefined.
In the second case, a User record is created in the database, and createdUser is assigned.

• Note that I'm aware of the following:

  In Mongoose 5, async operations [...] return a promise unless you pass a callback.

What is the expected behavior?
Both cases should create a record in the database and return the created record.

What are the versions of Node.js, Mongoose and MongoDB you are using?
Node.js: 12.16.1
MongoDB: 4.4.2
Mongoose: 5.11.9