Try using the dynamic recipients import from qlikview table object.
Then include the condition "If the object is empty" in the NPrinting job.
If the the above condition is met , the job fails at that step and stops sending email to the recipients list.
One way is the one I mentioned above.flag the not null values in separate field and include the condition in Nprintimg.
Another way is create a variable in Qlik for that field checking for empty filter.pull that variable into Nprintimg job condition while running the job.