How do I pass a null into a SP access through a DataContext?

I've got a stored procedure in SQL Server 2005 which allows for nulls to be passed in for some of the parameters.* The logic is written to allow for this, and I certainly want it that want.

I am new to using LINQ to SQL, and so I am trying to figure out how to pass a null in for some of the parameters to the strongly typed datacontext class that is created when I drag the SP onto the O/R designer in VS 2008.* For example, what do I use to pass in a null for a SQL Int value, to the method that corresponds to my stored procedure in my strongly typed datacontext class?