nvl function not working as expected

Hi,

I am using nvl function to replace null values to space. I tried both '' and ' ', but final value being inserted is still NULL.

I am inserting to Oracle table and I am using 4.0 SP2. nvl function is used in a query transform just prior to loading target.

nvl(field_name,'-') also not working, but nvl(field_name,'0') is working!!!.

Thanks in advance.

Sheshadri