(node:3341) DeprecationWarning: Mongoose: mpromise

I'm trying to develop a class on the top of the mongoose with my custom methods, so I extended the mongoose with my own class but when I invoke to create a new car method it works but its strip and error, here I let you see what I'm trying to do.

I'm getting this warning

(node:3341) DeprecationWarning: Mongoose: mpromise (mongoose's default promise library) is deprecated, plug in your own promise library instead: http://mongoosejs.com/docs/promises.html

after I do

driver.createCar({
      carName: 'jeep',
      availableSeats: 4,
    }, callback);

driver is an instance of Driver class

const carSchema = new Schema({
  carName: String,
  availableSeats: Number,
  createdOn: { type: Date, default: Date.now },
});
const driverSchema = new Schema({
 email: String,
 name: String,
 city: String,
 phoneNumber: String,
 cars: [carSchema],
 userId: {
   type: Schema.Types.ObjectId,
   required: true,
 },
createdOn: { type: Date, default: Date.now },
});
const DriverModel = mongoose.model('Driver', driverSchema);

class Driver extends DriverModel {
  getCurrentDate() {
  return moment().format();
}
create(cb) {
  // save driver
  this.createdOn = this.getCurrentDate();
  this.save(cb);
}
remove(cb) {
  super.remove({
  _id: this._id,
 }, cb);
}
createCar(carData, cb) {
  this.cars.push(carData);
  this.save(cb);
}
getCars() {
  return this.cars;
 }
}

any thoughts about what Im doing wrong?

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