You can always write:

   x : Result<string, err> = function...
   dangerous_function();
   switch(x) { 
     Ok() ... 
     Error() ...
   }

There's no difference between result and null other than readability (there's a mechanical transformation between the two, where you use unwrap() in rust on an unchecked null dereference, and you read errno in C instead of looking inside the Err() result variant).

To be clear, I strongly prefer Result<> because of the readability, but any dumb thing you can write with NULL + errno can be written with Result (and vice versa).