ADO.NET uses DBNull: http://msdn.microsoft.com/en-us/library/system.dbnull(v=vs.1...

There's one valid (if obscure) use case for it, other than that it is pretty much redundant: http://stackoverflow.com/q/4488727/1180426

All modern (micro)ORMs, even if they're just a thin wrapper over ADO.NET like Dapper, work just fine with regular nulls.