A None plus a NaR makes a None. Think of it as combining a “discard this” and a “causes problems if this isn’t discarded”.
If you’re using an None to calculate a load the load is skipped and you get another None on the belt. If you’re storing a None that’s a no-op.
But come to think of it, I’m not sure what happens when you use a NaR to do a load. Does it cause a fault immediately, or does it just drop a NaR on the belt?