This seems to be a CLJS specific issue - the above works fine in CLJ1.7.0-beta1. On the other hand, reductions too doesn't suffer this behavior (in CLJS):
I don't know, David - don't understand how this can be, since I just tried the same w/ 3269 and the extra `nil` still is happening (I first did use a clean setup as described in CLJS quickstart wiki). The below is from a figwheel REPL:
verified to still occur w/ 0.0-3269
I you want, I can attach a zip of my test project...
I wasn't quite careful enough when trying out your failing example. I see the problem, fix coming.