OK. I got a workaround for this issue.
I am first filtering the file so that I generate a csv file with the valid lines only, and in this way - making an empty file if there are no valid lines.
after that - I use the feature of the file adapter - Empty file handling - Do not create message - and that solves the problem.
However - it is still weird that this issue cannot be taken care of more elegantly...
If any one have a suggestion - I would like to hear it.
Thanks,
Imanuel Rahamim.