Nullable value types - C# reference

A nullable value type T? represents all values of its underlying value type T and an additional null value. For example, you can assign any of the following three values to a bool? variable: true, false, or null. An underlying value type T cannot be a nullable value type itself. Any nullable value type is an instance of the generic System.Nullable<T> structure. You can refer to a nullable value ty

[tgk]

型名に?をつけるとnullを代入できる