我无法在购物车路由器中填充该物品。该项目是ItemModel的实例

我想填充购物车路线中的项目，但无法填充。我无法在购物车路由器中填充该物品。该项目是ItemModel的实例。

ItemModel.js

const mongoose = require('mongoose');

const ItemSchema = new mongoose.Schema({
    subtaskItemName: {
        type: String,
        required: true,
        unique: true,
        trim: true
    },
    subtaskItemImage: {
        type: String
    },
    subtaskItemTime: {
        type: String
    },
    description: {
        type: String,
        trim: true
    },
    subtaskItemPrice: {
        type: String
    },
    subtaskItemStatus: {
        type: Boolean,
        default: true
    },
    subtask: {
        type: mongoose.Schema.ObjectId,
        ref: 'SubTask',
        required: true
    },
    createdAT: {
        type: Date,
        default: Date.now
    }

})

module.exports = mongoose.model("Item", ItemSchema);

CartModel.js

const monngose = require('mongoose');

const Schema = monngose.Schema;

const CartSchema = new Schema({
    user: {
        type: Schema.Types.ObjectId,
        ref: 'user'
    },
    task_items: [{
        task_item: {type:Schema.Types.ObjectId, ref: 'SubTaskCategoryItem'},
        quantity: { type: Number, default: 1 }

    }],
    totalPrice: {
        type: Number
    },
    item: {
        type: Schema.Types.ObjectId, 
        ref: 'Item'
    },
    crreated: {
        type: Date,
        default: Date.now
    }
});
module.exports = monngose.model('Cart', CartSchema);

CartRoute.js

const express = require('express');
const Cart = require('../../models/admin/CartModel');
const checkJwt = require('../../middleware/admin/user_auth');
const TaskItem = require('../../models/admin/ItemModel');

const router = express.Router();
  router.get('/get_cart', checkJwt, (req, res, next) => {

    Cart.find({ user:  req.user.id })
      .populate({
        path: 'user'
      })
      .populate('item')
    .exec((err, cart) => {
      res.json({
        msg: 'User not exists',
        cart: cart
      });

    })
  });

  module.exports = router;

如何在cart.js路由器中填充项目字段。我想填充购物车路线中的物品，但无法填充。我无法在购物车路由器中填充该物品。该项目是ItemModel的实例