How to trap Empty or Null in *STR() in BPC

Hi,

I am pulling data from a BW cube into a BPC apps.  BW cube has a field named 0PCODE, char(10)  that could be null in some

cases and mapped to  dimension PTCODE in the BPC app.  In the transformation, I need to check for NULL values  and map it accordingly.  I tried various approaches  as follows:

PTCODE = *IF( 0PCODE(1:10) = *STR() then "NOT-ASGND" ; 0PCODE)

PTCODE=*IF( 0PCODE(1:10) = *STR(0000000000) then "NOT-ASGND" ; 0PCODE)

PTCODE=*IF( 0PCODE = *STR(0000000000) then "NOT-ASGND" ; 0PCODE)

But nothing works and these mapping rule give "out of index/position" error.  Any idea how to handle this.

Thanks

DipM