nodejs mongoose : cyclic dependency detected - node.js

Question

I'm getting a cyclic dependency exception whereas I don't find any cyclic possibility in the very simple code at this point. I'm expecting it is happening due to population between two mongoose models but as said here : mongoose - possible circular dependency? this shouldn't produce this kind of error so I don't understand.
model\customer.js
var mongoose = require('mongoose'), Schema = mongoose.Schema;
var customerSchema = new Schema({
_siretCustomer:
{ type: String, required: true, minlength: 15, maxlength: 15, index: {unique: true} },
fileNumberCustomer:
{ type: String, required: true, minlength: 6, maxlength: 6 },
companyTypeCustomer:
{ type: String, required: true },
companyNameCustomer:
{ type: String, required: true },
contactName1Customer:
{ type: String, required: false, default: null },
contactName2Customer:
{ type: String, required: false, default: null },
landlineContact1Customer:
{ type: String, required: false, default: null },
landlineContact2Customer:
{ type: String, required: false, default: null },
emailContactCustomer:
{ type: String, required: false, default: null },
obligationCommentCustomer:
{ type: String, required: false, default: null },
taskCommentCustomer:
{ type: String, required: false, default: null },
creationDateCustomer:
{ type: Date, default: Date.now },
userCustomer:
[{ type: Schema.Types.ObjectId, ref: 'User', required: true }]
}, { collection: 'customer' });
module.exports = mongoose.model('Customer', customerSchema, 'customer');`
model\user.js
var mongoose = require('mongoose'), Schema = mongoose.Schema;
var userSchema = new Schema({
_trigramUser:
{ type: String, required: true, index: { unique: true } },
lastnameUser:
{ type: String, required: true },
firstnameUser:
{ type: String, required: true },
privilegeUser:
{ type: String, required: true, enum: ['Accountant', 'Social operator'] },
dateCreationUser:
{ type: Date, default: Date.now },
passwordUser:
{ type: String, required: true },
customersUser:
[{ type: String, ref: 'Customer'}]
}, { collection: 'user'});
module.exports = mongoose.model('User', userSchema, 'user');
controller\session\customerController.js
exports.readCustomer = (req, res) => {
database.getConnection();
customer.find(req).populate('userCustomer').exec((err, customer) => {
if (err) return res.status(500).json(err.stack);
res.status(200).json(customer);
});
};