We are generally not handling NIL right now. That was a convenience choice, since it made it a little easier to navigate when the spec was more unclear to me. Now I think we should add some handling.

Are we able to just add in a couple of ifs and whens, or do we need the condition system for this. The reason I ask is that all the errors should percolate upwards and be shipped to the end user, so we need a good way to do that.