I am trying to do an item filter within a DDR based on a presentation variable

When the variable is NUll - I need to display all the items

When the variable is not null I need to display the values passed in.

When I try to use a case statement it works for the NULL Value (all items are displayed)

But Fails when a selection list is sent in.

    and d.segment1 in

    (case

          when d.segment1 in is not null then (@{ITEM_SELECTION}['@']{''})

     else

       d.segment1

     end)

I have also tried this:

and d.segment1 in decode((@{ITEM_SELECTION}['@']{''}),null,d.segment1,(@{ITEM_SELECTION}['@']{''}))

Any Suggestions would be welcome.