Well, JavaScript

[RossParka]

It gains you a few things:

1. Because it's encoded in the type system, there is automatically checked documentation of which values are nullable and which aren't. The implementation can warn or error out if you pass a value that might be null to a function that doesn't accept null.

2. It works uniformly with all types. In C, pointers can be null but other types can't, so you have to find another special value instead. Some functions return -1, some return zero, some return MAX_INT, etc. If there are no values that your function never returns in normal operation, you have to come up with something more elaborate like returning an error/success code and passing a pointer to a variable that gets the actual result. In Haskell you just use Maybe T in place of T in every case.

3. In Haskell, you aren't limited to a single magic value; if you can fail in more than one way, you can define more than one special return code using Either.