companySchema.js

'use strict'
const mongoose = require('mongoose');
const Schema = mongoose.Schema;

let avaliationItemSchema = new Schema({
  description: String,
  _type: {type: Schema.Types.ObjectId, ref: 'avaliationType'},
  active: Boolean,
});

//SubDocuments referred qrcode will be genereted
let tagSchema = new Schema({
  name: String,
  description: String,
  active: Boolean,
  main: Boolean, //Describe what tag will be show when other methods company identification like (GPS)
  avaliationItems:[avaliationItemSchema]
});

let companySchema = new Schema({
  active: Boolean,
  deleted: Boolean,
  cnpj: String,
  ie: String,
  companyName: String,
  tradingName: String,
  urlLogo: String,
  address: {
    streetType: String,
    street: String,
    number: Number,
    complement: String,
    district: String,
    zipCode: Number,
    city: String,
    state: String,
    country: String
  },
  phone: String,
  emails: [String],
  tags: [tagSchema]
});

module.exports = mongoose.model('company', companySchema);

tenho uma função no meu controller para buscar uma company, e queria fazer um populate do atributo _type do Schema avaliationSchema, tentei assim mas não funcionou
const get = (uid) => { let query = {"_id": uid.toObjectId()}; return Model.findOne(query).populate('tags.avaliationItems._tagType'); };