Exception when accessing a type from another module

This exception occurs when trying to access types with arity > 1 from other modules. For instance, this example: ```Ocaml module M = struct type maybe_pair = | None | Pair of int * int end module N = struct let access_pair t = match t with | M.None -> () | M.Pair (x, y) -> () end ```` Raises the exception `Not_found`.