fix null warning

Program.cs

@@ -21,7 +21,7 @@ do
 
 Console.WriteLine($"Wygrana w {trials} próbie!");
 Console.Write("Podaj swoje imię: ");
-var name = Console.ReadLine();
+var name = Console.ReadLine() ?? "Jan";
 
 var hs = new HighScore { Name = name, Trials = trials };