I just completed the C# bowling exercise. This exercise is listed under Nullability. The only variable listed as nullable was the return value for Score (int?). I completed my exercise and didn’t have a need to use null in score. I looked at 3 of the pros examples and they don’t seem to use it. None of the tests check for nullability. If a game didn’t start or complete, we returned ArgumentException error. Did I fail to follow the instructions? https://exercism.org/tracks/csharp/exercises/bowling.