I'd like to sort my result like this:

• First I want all rows/objects where a column/property is not null, then all where the colmn/property is null.
• Then I want to sort by another column/property.

How can I do this with ICriteria? Do I have to create my own Order class, or can it be done with existing code?

ICriteria criteria = Session.CreateCriteria<MyClass>()
  .AddOrder(Order.Desc("NullableProperty")) // What do I do here? IProjection? Custom Order class?
  .AddOrder(Order.Asc("OtherProperty"));