Console stack error

https://stackoverflow.com/questions/47784425/ember-idx-accordion-throwing-console-error

I think this add-on looks great, but this ^  is happening on the first test after installing the addon. I've tried cleaning the npm and browser cache, uninstalling and reinstalling the addon. Thank you for taking the time to look at my issue.

Even some hints would be fine, I'm happy to keep on digging.