The Nullable<T> type is a C# construct that wraps around a non-nullable C# value type to allow the type to store an additional value--null--representing the absense of a value.
Nullable types are a value type in the FrooxEngine data model, but an Object in the ProtoFlux data model.
Nullable types are useful when one is unsure whether a value may or may not exist in the first place, rather than reling on some sort of default value that represents the absense of a value. In addition, whenever an "unset" state is useful to keep track of, nullables can come in handy.
See Also
- Microsoft's documentation on the nullable value types & nullable reference types.
- Wikipedia's definition of nullable types.