ember-changeset: Underlying object for changeset is missing...

(…but it’s not)

Version

ember-cli: 3.17.0 ember-changeset: 3.3.1 ember-cli-typescript: 3.1.3

Test Case

given: a component that expects a changeset as a property

import { module, test } from 'qunit'
import { setupRenderingTest } from 'ember-qunit'
import { render } from '@ember/test-helpers'
import { hbs } from 'ember-cli-htmlbars'

import Changeset from 'ember-changeset'

module('Integration | Component | my-component', function(hooks) {
  setupRenderingTest(hooks)

  test('it renders', async function(assert) {
    const obj = { bob: 'tom' }
    assert.ok(Boolean(obj), 'This should be true') // <- this, the same assert from the library, passes
    // @ts-ignore
    this.set('changeset', new Changeset(obj)) // <- this bombs with the above error
    // ...remainder of test ellided...
  })
})

(this is in a closed-source project; I can’t provide a link to the repo, but I can provide more information if you’d like)

Steps to reproduce

npx ember test

Expected Behavior

The test should continue, and render the component using the changeset.

Actual Behavior

The test fails on the indicated line above, with the error Error: Assertion Failed. Underlying object for changeset is missing.

It may be significant (or not) that the result is the same whether the file ends with .js or .ts; this doesn’t appear (to me) to be an Ember TypeScript edge case.