we should only assert if instanceof Error.
We may want to not assert and rather just console.error, as that gives us clickable stack. Assert gives us purple button debugging, but in this context and with the given stack that might not be worth it?

I've been often doing both in succession.

```javascript
if (reason instanceof Error) {
  Ember.logger.assert(...)
  Ember.logger.error(error.stack)
}
```