All of these birds have been imports. If a female lays infertile eggs, the male is at fault. This one is especially interesting. It is assumed almost universally as fact. The interesting thing is that, to the best of my knowledge, it has never appeared in print.
Nobody even knows who they originally heard it from.
I have yet to see any scientific basis for this assumption. In fact, with yellow napes specifically, I have proven to myself that it is more often the fault of the hen. Fifteen years of breeding yellow napes has given me quite a few opportunities to switch around birds. I have re-paired females that lay infertile eggs with males that have proven themselves fertile. At the same time, I have re-paired these supposedly sterile males with the producing females with which the other males have proven themselves.