static void PrintUserName(UserDetails? user) {
Console.WriteLine($"Name: {user?.Name ?? "No name"}, Age: {user?.Age.ToString() ?? "No age"}");
}
static void Test() {
PrintUserName(new UserDetails("Ben", 30)); // Prints "Name: Ben, Age: 30"
PrintUserName(null); // Prints "Name: No name, Age: No age"
}