Nullable reference types: How to specify “T?” type without constraining to class or struct

Question

I want to create a generic class that has a member of type T. T may be a class, a nullable class, a struct, or a nullable struct. So basically anyt

Answer 1

class Box {
    public T! Value { get; }

    public Box(T! value) {
        Value = value;
    }

    public static Box CreateDefault()
        => new default!;
}

What does null! statement mean?