Hi Matthias
This is very little information to analyse on. Are you able to provide the audit log for the module processing? Also, providing the whole source code or some of the other lines before and after the two lines above would provide more context to the logic of the module.
If you can't, then I'd suggest you add additional statements to output the values of the variables to the audit log.
Another alternative I'd suggest is to try and perform standalone testing of the module logic in NWDS/Eclipse before deploying it on the server and testing end to end. Refer my blog below on how this can be achieved.
Standalone testing of Adapter Module in NWDS
Regards
Eng Swee