In Rust (and Haskell and OCaml for that matter), there is no built-in null keyword. Option is just an enum in the library that happens to have a variant called None. So it's technically Option::None and Option::Some(x). But, really, it could be Quux and Quux::Bla and Quux::Boo(x) instead--without any language changes.

That is vastly better that what IntelliJ does for Java with their weird @NonNull annotations on references--which technically still can be the null. null is still a keyword there, and null is somehow a member of every reference type (but not of the other types--how arbitrary).

And C# has a null keyword, and the rules for type autoconverting it are complicated, and some things you just aren't allowed to do with null (even though they should be possible according to the rules) because then you'd see what mess they made there (you'd otherwise be able to figure out what the type of null is--and there's no "the" type there. null is basically still a member of every type. And that is bad).

So even the language used in "allowing values to be nullable by default" is insinuating a bad idea. Nullability is not necessarily a property that needs to exist on values in the first place (as far as the programming language is concerned).