Qunit serializer test is returning "Cannot read property 'push' of null"

Ember serializer test below is failing at line 103, throwing the error shown above it:

FYI, I am using the Pretender library to create a response from the server.

Looks like it has something to do with relationships. What does your model look like? And have you handled relationship data with pretender as well?

Interestingly, even when I remove all of the relationships of assignment on both the model and the serializer, this error is still thrown. So I don’t think the error is related to the relationships of this particular payload.

Here is the code:

assignment model:

import DS from 'ember-data';
const {
} = DS;

export default Model.extend({
	title: attr('string'),
	submissionType: attr('string'),
	description: attr('string'),
	completed: attr('boolean'),
	displayType: attr('string'),
	dateOfCreation: attr('string'),
	lastUpdate: attr('string'),
	autopass: attr('boolean'),
	moduleItem: attr('object')

assigment serializer:

import DS from 'ember-data';
const { JSONAPISerializer } = DS;

export default JSONAPISerializer.extend({
	attrs: {
		autoPassReviewerNote: 'autoPassReviewerNote',
		dateOfCreation: 'date_of_creation',
		displayType: 'displayType',
		lastUpdate: 'last_update',
		moduleItem: 'moduleItem',
		submissionType: 'submissionType'

assignment serializer test:

import { moduleForModel, test } from 'ember-qunit';
import Pretender from 'pretender';
import Ember from 'ember';

const {
} = Ember;

var server;

moduleForModel('assignment', 'Unit | Serializer | assignment', {
	needs: [

	beforeEach: function() {
		server = new Pretender(function() {
			// eslint-disable-next-line ember/use-ember-get-and-set
			this.get('/assignments/:id', function() {
				var response = {
					data: {
						type: 'assignment',
						id: 98,
						attributes: {
							title: 'dfgdfg',
							submissionType: 'dfgdf',
							displayType: 'dfgdfg',
							date_of_creation: 'sdfgsdfg',
							last_update: 'fgdgd'

				return [ 200, { 'Content-Type': 'application/json' }, JSON.stringify(response) ];

	afterEach: function() {

test('testing assignment serializer', function(assert) {
	var checkAttrSerialization = (assignment) => {
		assert.equal(assignment, true);

	let store = this.store();

	run(() => {
		return store.findRecord('assignment', 98).then((assignment) => checkAttrSerialization(assignment));