这是密码

app.get("/cart", checkAuthentication, function (req, res) {

  Orders.find({ user: req.user._id })
    .populate('user')
    .populate('order')
    .exec((err, orders) => {
      console.log(orders);
        if (err) {
          console.log("ERROR /cart :\n" + err);
          res.redirect("/");
        } else {

          const OrderList = [];

          orders.forEach((order) => {
            const obj = {
              order: order.order,
              id: order._id
            }
            
            OrderList.push(obj);
          });

          var sum=0
          OrderList.forEach(function(item){ 
            sum += item.order.price 
          });

          req.session.sum = sum;
          req.session.orders = OrderList;

          res.render("cart", {  itemList: OrderList, login: true, name: req.user.name });
            // res.render("cart", {  itemList: OrderList, login: false, name: "abc" });
        }
    });
});

这是订单模型=〉

const mongoose = require("mongoose");
const Schema = mongoose.Schema;

const orderSchema = new Schema({
  user: { type: Schema.Types.ObjectId, ref: "User" },
  order: { type: Schema.Types.ObjectId, ref: "SellingItem" },
  date: { type: Date, default: Date.now }
});

module.exports = mongoose.model("Orders", orderSchema);

这就是错误
ERROR(null)
这是我的存储库的github链接-https://github.com/Paras0750/Bakery_Website/
我正在尝试填充订单字段，但它显示为空。