Better stack trace for the following error

[craig-dae]

I had a bug that I recently squashed, where I had a switch-case in a switchMap, but neither of my two switch conditions happened, so I returned nothing. I recieved an error that began with the following:
ERROR Error: Uncaught (in promise): TypeError: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.

The stack trace provided nothing useful to find where my mistake was. It burned maybe two hours narrowing it down to the offending observable before figuring out the problem. If a switchMap doesn't return an observable, can you please provide some way of letting the developer know which switchMap created the problem?

Thanks