The only problem is... only a couple of nulls have assault to begin with. The others aren’t skills you’d ever be running in your grid under normal circumstances, and honestly I don’t see why you’d want to run them here either.
On the other hand, it’s hella easier to just use SR filler for 1 slot compared to another MLB null.
Have I seen DMM players that run or consider double null as a filler option...? Answer’s no. Not that I know of.