JDBC adapter insert failure

I am trying to pass the values from a document list to an insert adapter service. Now when I do a one to one mapping of the values, it gives me a run time error “failed to copy values to … from …”
When I map the whole document to the insert service input instead of mapping each element, then it passes the vales to input properly but then i get an error “unable to insert record in database. Null values not allowed”.
Now if i trace the pipeline, i do not see any elements with null values.
Any idea why i am getting this error ? Is there any other way of passing values to the adapter service.