Comparison of null `Nullable`s

[Luís Marques via Digitalmars-d]

Have you considered making these work, instead of throwing an 
exception?

    import std.typecons;
    alias T = Nullable!(int, -1);

    void main()
    {
        T a;
        T b;
        assert(a == b);

        T c;
        T d = 42;
        assert(c != d);
    }

It could be a template parameter for Nullable, and the default be 
to preserve the current behavior.