async get(id) {
    let user;

    if (mongoose.Types.ObjectId.isValid(id)) {
      user = await this.findById(id).exec();
    }
    if (user) {
      return user;
    }

    throw new APIError({
      message: 'User does not exist',
      status: httpStatus.NOT_FOUND,
    });
  }
Get user

@param {ObjectId} id - The objectId of user.
@returns {Promise<User, APIError>}