Option

If you want null-able Values, Option is very suitable. For any type T, Option<T> is valid type and it is null-able. Null Value can be denoted as None.

let name: Option<String> = None;

In other hand, not null Values for null-able are denoted with Some(_).

let name: Option<String> = Some("MGR");

Some is considered as a natural transformation T -> Option<T> representing not null Values.