TypeError: (intermediate value).populate(...).exec is not a function

Возникает ошибка TypeError: (intermediate value).populate(...).exec is not a function, когда я хочу использователь populate

    const user = await UserModel.findById(req.userId);
    const doc = new contactUserModel({
      user: user,
      telegram: req.body.telegram,
      whatsUp: req.body.whatsUp,
      vk: req.body.vk,
      phoneNumber: req.body.phoneNumber,
      facebook: req.body.facebook,
    }).populate('user').exec();

Схема контакта:

const contactUserSchema = new mongoose.Schema({
    user: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'User',
        required: true,
    },
    telegram: {
        type: String,
    },
    whatsUp: {
        type: String,
    },
    vk: {
        type: String,
    },
    phoneNumber: {
        type: Number,
    },
    facebook: {
        type: String,
    },
},  
);

export default mongoose.model('contactUser', contactUserSchema);

C чем это может быть связано?