Nullable/Non-nullable reference types in C# 8.0 having nothing to do with Nullable<T> and aren't even implemented using it.
C# 8.0 implementation of something like Optional<T> for reference types uses static flow analysis to ensure correct use of potentially null values. That's vastly superior in every way to Optional<T>.
[dead]
Yes, because it's checked by the compiler using normal constructs.
someNullableInstance.DoSomething(); // compiler error
if (someNullableInstance != null)
someNullableInstance.DoSomething(); // not an error
Am I? Apparently so is everyone else because Microsoft has re-worked Nullable<T> in C# 8 to be almost exactly like Java Optional! Silly me right?