In those circumstances you don't need a generic null reference, you just need a sentinel, which can be typed. A null reference is a conflation of several distinct notions. e.g., in poor layman's terms, uninitialized, missing, nothing-to-see-here, not-in-set, etc. A computational statistics professor once tried to explain to me the formal distinctions (including a new one he was proposing), but at the time I didn't grasp the importance and subtlety; all I remember now--a decade later--is that I wish I paid better attention.
I'm not exactly sure what is gained from removing generic null references entirely, though.