I don't really know what's triggering this on my server, but based on the countless warnings filling my console, I'm guessing it has something to do with an egg loaded in a dispenser.

2.8b582 on spigot server 1.7.9

08.01 12:19:24 [Server] INFO MessageAction: getShooter = null, this shouldn't happen. (PROJECTILE_EGG@DISPENSER)