It's worth noting that having a NULL, somewhere, is not so much a problem as forcing types to have a NULL. In this respect, e.g. Python and Rust both get it right: while Python has a None, and Rust has std::ptr::null(), an object that is a string cannot be any of those, because those are different types (NoneType and raw pointer, respectively). C's problem is that a string could be null, and there's no syntax for a non-null string.

Python's problem, meanwhile, is that any parameter could be any type. In C, you can pass NULL to a function expecting a non-null string. In Python, you can also pass 42, [], or the sqlalchemy module. None isn't special here. :)

Also, to quibble a bit: Rust's std::ptr::null() is just a raw pointer, and isn't actually usable in safe Rust. Actual safe pointer types are guaranteed non-null and you'd use Option<&T> to specify that they're nullable. Raw pointers cannot be dereferenced in safe Rust. It is true that std::ptr::null() is in Rust's standard library, but Foreign.Ptr.nullPtr is in Haskell's, and the purpose is the same (a special raw-pointer type only used for FFI purposes), so Rust isn't any worse than Haskell here.