Invert Boolean Replaces Nulls

I’m working through a sift-pattern to cull some linework (seams) before rejoining some curves. It seems that the invert boolean is replacing the existing nulls with ‘True’ or ‘1.’ Is this expected behavior?

Of course I can rewrite the greater-than/lesser-than filter to avoid the invert-boolean component, (or clean the tree first–but then I can’t recombine) but I thought I’d point this out & inquire.