C#. Until semi-recently it was only used for value types (as reference types are supposed to be nullable by default) but these days you can enable explicit nullables, which means that you have to explicitly specify nullability even for reference types.

I like explicit nullables. It’s not much more work to type those question marks and it adds a safeguard against null showing up where it shouldn’t.

I specifically inspired insisted on it for this picture because the code on the sign uses capitalized names for something that isn’t a class, which is a very C# thing to do.

That should be private string? Gender. Explicit nullables are your friends.