OLAP Drillthrough For Null Data

Hi:

The drillthrough in my cube is working fine except for the cases where the dimension member is null. For example I have the dimension
PRODUCT (dim)
- PROD_TYPE_CD (name = PROD_TYPE_CD || '-' || PROD_TYPE_NM)
- PROD_CD
-PROD_NM

So for if the data is like the following where the PROD_TYPE_CD is null :
- (name = -FOOD)
- 123
- bread

The drillthough is not displaying any data no matter I select the PROD_TYPE_CD, PROD_CD or PROD_NM in the dimension drop down altough if query the DB directly I found data to display in the drillthrough
Any ideas why this is happening and how to solve it.

Thanks
J