I don't understand it! It seems that in older quests that were made before the guy enemy class was removed, null type enemies with sprites defined are fully visible, while in newer quests, they are invisible regardless of whether or not you select a sprite for them!

And this bit of info from the change log seems to be meaningless:
Seemingly fixed a bug where null enemies were being instantiated and not being put in the guy list... presumably causing a memory leak.
Because none of the null enemies in the enemy editor are even listed in the guy list! As a matter of fact, I think it would be better if we could at least edit the default guys in the guy list via the enemy editor.