Dynamically adding Where parameters to LinqDataSource on nullable column

Question

I am dynamically adding a where parameter to a LinqDataSource that binds a GridView.

Parameter p1 = new Parameter { Name = "Param1", Type = TypeCode.DateTime, DefaultValue = DateTime.Now.ToShortDateString() } ;
MyLinqDataSource.WhereParameters.Add(p1);                    
MyLinqDataSource.Where = "EndDate >= @Param1";

This works, but the EndDate column above is actually nullable (meaning 'open-ended'). How can I include the rows with null as an EndDate value in my resultset?