> My understanding is that JVMs implement this by (a) representing Java `null` references as the zero pointer, (b) mapping the zero page with write permission disabled

If you want to run everywhere where C does, you can't rely on that. I gave WASM as an example - that's a widely used target that just exposes a flat memory model where 0 is literally just a normal address and there's no way to trap it (unless they've released extensions I'm unaware of). Same deal with most microcontrollers as far as I'm aware of, although I don't do embedded.

I can't think of a way you'd implement null trapping efficiently on those platforms.