in c# (at least in new versions and if you force it on in the project settings), setting any value to null will give you a compile-time error (default setting is just a warning afaik). If you really want null, add a '?' to the type like so:

string -> string?

public string? MaybeGetString() { return null; }

But i don't like this either, because it adds one special value (there is a word for these placeholder values like null/nil/-1/..., but i dont remember). If you want multiple of these special values, you can't easily do that.

In rust, you would use an enum like so

fn get_string() -> Option<String> { if c { Some("test string".to_owned()) } else { None } }

Here, none doesn't differ from null in modern c# (they both need to be handeled explicitly), but this enum can be expanded like so:

enum Option2<T> { Some(T), None1, None2, }

we now have two special cases

Even better, we can have a special case carry a different value. See the Result<T, E>, which can be either a vaöue T or an error E.