I get the above error when I try the following code?

I'm a newbie so what am I missing? TIA.

The table has only 2 fields. swst_pk, and stock. Both are integer and don't allow nulls.

I also tried playing with Return Alternate on Null in the BO Mapper but could not get that working. Also, played with AllowNullValueonNewRow in the properties using both True and False and did not get that to work either. My version of SF is 1.6.6.0