There’s no qualitative difference for Final Smash, because each effect on a spell looks for targets in isolation from the others. There’s never anything stopping you from playing a card that won’t do anything. This is in official rulings, so asking us to reconsider it is moot.
In times of statically-typed languages, any time a card needs to affect something, that target can be nothing (Option / Maybe). Depending on how you implemented “if you do, …” effects, you might have to do this anyway.
Maybe this is something to discuss in the rules thread instead?