TypeError: Cannot read property 'length' of null doesn't make sense

I keep getting a TypeError: Cannot read property 'length' of null and it doesn't make sense why it's throwing..

Test:

await render(hbs``);

assert.equal(this.element.querySelector('div.card-details div#summary').length, 1);

await click('.card-details__show-more-link');

assert.equal(this.get('isExpanded'), true);

Compiled .hbs file for card-details: