handle case of null Stack::pushEvent in CallEvent ctor
handle case of null Stack::pushEvent in CallEvent ctor

MaartenR/avian,bigfatbrowncat/avian-pack.avian,ucdseniordesign/avian,bgould/avian,getlantern/avian,bigfatbrowncat/avian-pack.avian,dicej/avian,bgould/avian,badlogic/avian,joshuawarner32/avian,dicej/avian,marcinolawski/avian,lostdj/avian,minor-jason/avian,MaartenR/avian,badlogic/avian,minor-jason/avian,MaartenR/avian,joshuawarner32/avian,lwahlmeier/avian,joshuawarner32/avian,marcinolawski/avian,ucdseniordesign/avian,lostdj/avian,badlogic/avian,lostdj/avian,dicej/avian,lostdj/avian,joshuawarner32/avian,MaartenR/avian,ucdseniordesign/avian,lwahlmeier/avian,bigfatbrowncat/avian-pack.avian,marcinolawski/avian,bgould/avian,minor-jason/avian,badlogic/avian,marcinolawski/avian,ucdseniordesign/avian,getlantern/avian,getlantern/avian,bigfatbrowncat/avian-pack.avian,dicej/avian,getlantern/avian,lwahlmeier/avian,bgould/avian,minor-jason/avian,lwahlmeier/avian