I\'ve read many of the non-nullable questions and answers. It looks like the best way to get close to non-nullable types in C# (4.0) is Jon Skeet\'s NonNullable<> hack.<
Yep, spec#: http://research.microsoft.com/en-us/projects/specsharp/
-- Edit: I just noticed you said C# 4.0; I'm fairly sure Spec# doesn't support that version. Nevertheless, it's worth a review.
You may also be able (I think) to check at a slightly later stage then compile, via a rule in Gendarme: http://www.mono-project.com/Gendarme (assuming that runs against 4.0)
I've run into this a few times...I've yet to find anything better than Skeet's solution. It's solved all the cases I've come across, so I have to give it my vote.
I agree it's a bit of a hacky situation that we have to resort to that...but his fix does solve the problem.