Mongoose way to get array to default to null

index.test.js

const assert = require('assert');
const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/test-mongoose-default-null');

describe('mongoose', function () {
  for (const {id, buildSchema, } of [
    {
      id: 'FooNull',
      buildSchema: () => new mongoose.Schema({
        bar: {
      type: [Number, ],
      default: null,
      },
      }),
    },
    {
      id: 'FooUndefined',
      buildSchema: () => new mongoose.Schema({
        bar: {
          type: [Number, ],
          default: undefined,
        },
      }),
    },
    {
      id: 'FooQueue',
      buildSchema: () => {
        const FooSchema = new mongoose.Schema({
          bar: {
            type: [Number, ],
          },
        });
        FooSchema.methods.postconstructed = function () {
          this.bar = null;
        };
        FooSchema.queue('postconstructed');
        return FooSchema;
      },
    },
  ]) {
    it(`should allow default:null for array (${id})`, async function () {
      const FooSchema = buildSchema();
      const Foo = mongoose.model(id, FooSchema);
      const foo = new Foo();
      assert.strictEqual(foo.bar, null);
      await foo.save();
      const loadedFoo = await Foo.findById(foo._id);
      assert.strictEqual(loadedFoo.bar, null);
    });
  }
});

output.txt

ohnobinki@gibby ~/mongoose-defaultnull-play $ ./node_modules/.bin/mocha index.test.js


(node:5768) DeprecationWarning: `open()` is deprecated in mongoose >= 4.11.0, use `openUri()` instead, or set the `useMongoClient` option if using `connect()` or `createConnection()`. See http://mongoosejs.com/docs/connections.html#use-mongo-client
  mongoose
    1) should allow default:null for array (FooNull)
    2) should allow default:null for array (FooUndefined)
(node:5768) DeprecationWarning: Mongoose: mpromise (mongoose's default promise library) is deprecated, plug in your own promise library instead: http://mongoosejs.com/docs/promises.html
    ✓ should allow default:null for array (FooQueue)


  1 passing (95ms)
  2 failing

  1) mongoose should allow default:null for array (FooNull):
     AssertionError [ERR_ASSERTION]: [] === null
      at Context.<anonymous> (index.test.js:46:14)

  2) mongoose should allow default:null for array (FooUndefined):
     AssertionError [ERR_ASSERTION]: undefined === null
      at Context.<anonymous> (index.test.js:46:14)