Capture blank/null in IDT

Hi,

My universe in IDT is designed to capture records from seven different dim tables in SQL Server. Unfortunately some of the records or fields are blank and showing up as blank in the webi report. I tried putting ISNULL in webi but did not work. How can I put the ISNULL in IDT? Previously there is an option of inserting 0 for undefined for each object. I don't see that in the IDT, may be I am missing something.

Appreciate your suggestion.

Arun