Fix PrincipalField when selecting an external user
Fix PrincipalField when selecting an external user

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