static assert(isNullable!(const Nullable!(int, string)));
static assert(isNullable!(Nullable!()));
static assert(!isNullable!(Variant!()));
static assert(!isNullable!(Variant!string));
static assert(!isNullable!int);
static assert(!isNullable!string);
Checks if the type is instance of Algebraic with a self TypeSet that contains typeof(null).