There is a more indirect way of combating them, although it would take some information gathering and you would likely need to involve at least a small elite team of your current hosts to do it.

[She's fine with offering Hope logical suggestions. She's the one with the combat experience, and it never hurts to be on pleasant terms with the god who resurrects everyone. Hope is actually fairly pleasant once one gets to know him a little. He just needs to work on his public relations skills a LOT. So do most of the gods, really.]

In order to produce more of their kind, they must have factories to build more. Find out where those factories are, and destroy them. If possible, capture one Null and determine exactly how it communicates with the others. Then spread misinformation to all of them. If you are fortunate, you could feed them false information about your whereabouts, lure a large number of them to an uninhabited place, and then destroy that.