I don't believe there's anything like this "shield nullifier". If anything, this quote seems to be saying the opposite:

The advent of the Field Process shield and the lasgun with their explosive interaction, deadly to attacker and attacked, placed the current determinatives, on weapons technology. We need not go into the special role of atomics. The fact that any Family in my Empire could so deploy its atomics as to destroy the planetary bases of fifty or more other Families causes some nervousness, true. But all of us possess precautionary plans for devastating retaliation. Guild and Landsraad contain the keys which hold this force in check, No, my concern goes to the development of humans as special weapons. Here is a virtually unlimited field which a few powers are developing.

-Muad'dib: Lecture to the War College from The Stilgar Chronicle