Thanks for the long file name answer. It saves me work looking at trying to fix it.
Any ret would probably work, but as it current stood it was pointing off into nowhere, hence the crash when set_zoom_speed was referenced. The location of nullsub_1 is probably static across all versions so far... it maps to a BX LR, essentially a ret instruction.
The NULLSUB macro would make more sense. I'll take a look at changing that, but I'm going to be pretty busy for the next two weeks.