do nothing if specificSources is falsy
do nothing if specificSources is falsy

MeteorAdminz/fullcalendar,blubberly/fullcalendar,rgnevashev/fullcalendar,MeteorAdminz/fullcalendar,kleisauke/fullcalendar,blubberly/fullcalendar,deepskyr/fullcalendar,deepskyr/fullcalendar,oleg-babintsev/fullcalendar,fullcalendar/fullcalendar,laoneo/fullcalendar,kleisauke/fullcalendar,MeteorAdminz/fullcalendar,arshaw/fullcalendar,laoneo/fullcalendar,oleg-babintsev/fullcalendar,MeteorAdminz/fullcalendar,rgnevashev/fullcalendar,arshaw/fullcalendar,kleisauke/fullcalendar,fullcalendar/fullcalendar,fullcalendar/fullcalendar,arshaw/fullcalendar,avanti-technologies/fullcalendar,laoneo/fullcalendar,deepskyr/fullcalendar,pietervisser/fullcalendar,rgnevashev/fullcalendar,fullcalendar/fullcalendar,pietervisser/fullcalendar,kleisauke/fullcalendar,blubberly/fullcalendar,deepskyr/fullcalendar,avanti-technologies/fullcalendar,arshaw/fullcalendar,rgnevashev/fullcalendar,avanti-technologies/fullcalendar,blubberly/fullcalendar,oleg-babintsev/fullcalendar,avanti-technologies/fullcalendar,pietervisser/fullcalendar