Fix agreement user property: user_id can be 0
Fix agreement user property: user_id can be 0

ThiefMaster/indico,DirkHoffmann/indico,ThiefMaster/indico,mic4ael/indico,ThiefMaster/indico,mic4ael/indico,DirkHoffmann/indico,indico/indico,mvidalgarcia/indico,mvidalgarcia/indico,OmeGak/indico,OmeGak/indico,ThiefMaster/indico,DirkHoffmann/indico,indico/indico,indico/indico,OmeGak/indico,indico/indico,OmeGak/indico,mvidalgarcia/indico,mic4ael/indico,pferreir/indico,mic4ael/indico,pferreir/indico,DirkHoffmann/indico,mvidalgarcia/indico,pferreir/indico,pferreir/indico