private enum XXX {
        ETT = 1,
        TVA = 2
    } ;


    protected void Page_Load(object sender, EventArgs e)
    {
        XXX v;
        XXX? v2;
        v = (XXX)1;
        v2 = (XXX?)2;
        v2 = Convert.ChangeType(2, typeof (XXX?));
    }