static void Main(string[] args)
{
Console.WriteLine("Hello World!");
PersonType?type = PersonType.x;
PersonType?type2 = null;
PersonType type3 = PersonType.x;
Console.WriteLine(default(PersonType?) == null);
Console.WriteLine(type2.IsDefault());
Console.WriteLine(type2.GetValueOrDefault().IsDefault());
Console.WriteLine(type3.IsDefault());
Console.ReadKey();
}
