Random Question - Can you fight a gym with less than six Pokémon?

So, either a new account built to Level five by spinning stops only, having a Pokémon as your buddy, having up to twenty Pokémon in gyms and transferring Pokémon - it's possible (but unlikely) to have less than six available Pokémon to battle in your inventory - it's even possible to have ZERO.

I'm curious what battling a gym in this circumstance does. Anyone have any experience? Didn't we have a member who's significant other deleted all of his Pokémon? Anyone have the ability to test this? I guess I could create a second account and push it to Level 5 pretty quickly... but that sounds like effort (also, against the TOS) when someone here might already have an answer. ;)