var a = new int?();
int? b = null;
int? c = new int?();
int? d = new();
Console.WriteLine(nameof(a) + " - has value " + a.HasValue + " - Value " + a);
Console.WriteLine(nameof(b) + " - has value " + b.HasValue + " - Value " + b);
Console.WriteLine(nameof(c) + " - has value " + c.HasValue + " - Value " + c);
Console.WriteLine(nameof(d) + " - has value " + d.HasValue + " - Value " + d);

Output
a - has value False - Value
b - has value False - Value
c - has value False - Value
d - has value True - Value 0