Issue with To_number Conversion when we submit Shipping report from Document set

 Hi All

We have a report in Shipping responsibility which works fine when we submit from Standard Request form, when we submit through Document set we are getting error
as Invalid Number for to_number conversion in formula columns which is ok from sql developer

begin
  select  to_number(rtrim(ltrim(nvl(attribute6 ,'0') )))     into v_gross_weight
  from wsh_new_deliveries
  where delivery_id = to_number(:pick_slip_number);

Any hints for fixing this will be helpfull

Thanks
Kamalakar.G