C# Enums: Nullable or 'Unknown' Value?

Question

If I have a class with an enum member and I want to be able to represent situations where this member is not defined, which is it better?

a) Declare the

Answer 1

I agree with archimed7592 that there is a real difference between absent value and "Unknown" value.

Example:

"what is your blood type?"

• Null = absent value --> question hasn't been answered --> ask the question

• "Unknown" --> patient indicates he doesn't know --> order lab test for the blood type