Ember cannot read property 'find' of undefined

We just installed an error-tracker for our Ember-application, and the only error that is reported is Cannot read property 'find' of undefined. The code that cause this error is within a component, and looks like this:

this.$().find('.countdown-number').text(current);

I don't understand how this can happen. How can $() be undefined, since it's a part of the ember framework?

According to the error-tracker, it happens for a bunch of different browsers, latest Chrome for example. I however can't reproduce the error in any browser.

I know this isn't the "ember way" of updating a text in a div, but I would prefer to not have to rebuild a lot, I just want to fix the bug with as little changes as possible.