猫鼬：TypeError：无法读取未定义的属性“ findOne”

我正在使用node.js进行结算，并创建了一个新模型Stripecustomer，用于保存stripe customer id和该客户的email。我从其他猫鼬模型中复制了主要代码并进行了更改。我曾希望立即开始使用它，但是当我尝试在此模型中查找文档时，出现以下错误：

⛔️ Error:
 TypeError: Cannot read property 'findOne' of undefined

我已经看了半个小时，看不到我做错了什么。谁能告诉我我做错了什么地方？

workspace.controller.js：这是我尝试创建订阅的地方。Stripecustomer是未定义的，但是我不知道为什么，因为我将其导入到顶部

const stripe = require("stripe")("sk_test_dvebbZQPA4Vk8kKZaEuN32sD");
const {
  Group, User, Workspace, Stripecustomer
} = require('../models');
const { sendErr } = require('../../utils');



const billing = async (req, res) => {
  try {
    const email = '[email protected]';

    // get the payment plan
    const plan = await stripe.plans.retrieve('plan_EK1uRUJLJcDS6e');

    //   get the stripe customer or create a new one
      let customer;
    const existingCustomerDoc = await Stripecustomer.findOne({ email: email });

    // if we couldn't find an existing customer in our database...
    if (!existingCustomerDoc[0]) {
      // then we create a new customer
      customer = await stripe.customers.create({
        email,
        source: 'src_18eYalAHEMiOZZp1l9ZTjSU0'
      });
    } else {
    //  we retrieve this customer in stripe
      customer = await stripe.customers.retrieve(existingCustomerDoc.customer_id);
    }

    // subscribe the customer to the plan
    // You now have a customer subscribed to a plan.
    // Behind the scenes, Stripe creates an invoice for every billing cycle.
    // The invoice outlines what the customer owes, reflects when they will be or were charged, and tracks the payment status.
    // You can even add additional items to an invoice to factor in one-off charges like setup fees.
    const subscription = await stripe.subscriptions.create({
      customer: customer.id,
      items: [{ plan: plan.id }]
    });


    res.status(200).json({
      message: 'payment complete',
      obj: subscription
    });
  } catch (err) {
    return sendErr(res, err);
  }
};

stripecustomer.model.js

const mongoose = require('mongoose');

const { Schema } = mongoose;

const stripeCustomerSchema = new Schema({
  email: {
    type: String,
    required: true
  },
  customer_id: {
    type: String,
    required: true
  }
});

const Stripecustomer = mongoose.model('Stripecustomer', stripeCustomerSchema);

module.exports = Stripecustomer;