I know you're replying to a brand new (likely troll) account, but I'm also very confused by this and would be curious to learn if there's any truth to it. I personally don't really see what a Von Neumann machine has to do with null pointers (or how an implication would go either way), but maybe I'm missing something.
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NULL pointers working the way they do was a design decision made my hardware engineers a long time ago because it saved some transistors when that mattered. We’re past that point now for most ASICs and hardware can be changed. Although backward software compatibility is a thing too.
It has nothing to do with NULL pointers and is instead a property of a programming language.