Mongoose 5.7.5 breaking cloning

[dawnmessier]

BUG

Using

• NodeJs 12.12.0
• Mongoose 5.7.5
• MongoDb 3.3.3

I have a pre-existing module for cloning a schema which is used to back up web pages (like a CMS system). When I upgraded to mongoose 5.7.5 (from 5.5.2), the schema cloning broke.

this is the cloning module:

    module.exports = function (schema, mongoose) {
    'use strict';

    mongoose = mongoose || require('mongoose');

    let clonedSchema = new mongoose.Schema();

    schema.eachPath(function (key, path) {
        if (key === '_id') {
            return;
        }

        let clonedPath = {};

        clonedPath[key] = path.options;
        delete clonedPath[key].unique;

        clonedSchema.add(clonedPath);
    });

    return clonedSchema;
    };

this is the schema getting cloned

    let pageSchema = new Schema({
    title: {
        type: String,
        required: true
    },
    translateKey: {
        type: String,
        required: true
    },
    lang: {
        type: String,
        required: true
    }
    },
    {
    timestamps: true
    });

It's breaking on clonedSchema.add(clonedPath) with the first path it tries to add.

ERROR

    UnhandledPromiseRejectionWarning: MongooseError: Invalid ref at path "title". Got null
    at new MongooseError (/node_modules/mongoose/lib/error/mongooseError.js:10:11)
    at validateRef (/node_modules/mongoose/lib/helpers/populate/validateRef.js:17:9)
    at Clone.Schema.path (/node_modules/mongoose/lib/schema.js:577:5)
    at Clone.add (/node_modules/mongoose/lib/schema.js:442:12)
    at Schema.extend (/node_modules/mongoose-schema-extend/index.js:81:13)
    at /api/common/lib/clone-schema.js:19:22
    at Schema.eachPath (/api/node_modules/mongoose/lib/schema.js:934:5)
    at module.exports (/api/common/lib/clone-schema.js:9:12)
    at Object.<anonymous> (/api/common/schemas/Page.schema.js:39:23)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)

I did a comparison of the schema passed into this module between mongoose 5.5.2 and 5.7.5. The only difference in 5.7.5 is that $immutable is now an included property

    title: 
      SchemaString {
        enumValues: [],
        regExp: null,
        path: 'title',
        instance: 'String',
        validators: [Array],
        getters: [],
        setters: [],
        options: [Object],
        _index: null,
        '$immutable': null,
        isRequired: true,
        requiredValidator: [Function],
        originalRequiredValue: true,
        [Symbol(mongoose#schemaType)]: true },
     translateKey: 
      SchemaString {
        enumValues: [],
        regExp: null,
        path: 'translateKey',
        instance: 'String',
        validators: [Array],
        getters: [],
        setters: [],
        options: [Object],
        _index: null,
        '$immutable': null,
        isRequired: true,
        requiredValidator: [Function],
        originalRequiredValue: true,
        [Symbol(mongoose#schemaType)]: true }

I tried "npm mongoose-schema-extend", but that gave me TypeError: Method Map.prototype.has called on incompatible receiver [object Map]. So not sure how to use it here.

    const extend = require('mongoose-schema-extend');

    let clonedSchema = new mongoose.Schema();

    schema.eachPath(function (key, path) {
        if (key === '_id') {
            return;
        }

        let prop = {};
        prop[key] = path;
        clonedSchema.extend(prop);
    });

I threw a try/catch into the module to see if that would do anything. Nope.

I also deleted the node_modules directory and re-installed the plugins.

I also added useUnifiedTopology: true to Mongoose initialization for posterity.

Does anyone know what changed in 5.7 to break this?