initialize last_containers to empty list
initialize last_containers to empty list

Only call `containers` in `begin`/`rescue` block

airbnb/synapse,dallasmarlow/synapse,asiragusa/synapse,democracyworks/synapse,jolynch/synapse,StephanErb/synapse,bobtfish/synapse,bobtfish/synapse,bcicen/synapse,freiheit-com/synapse,lsjostro/synapse,gini/synapse,EasonYi/synapse,tdooner/synapse,yonglehou/synapse-1,claydotio/synapse,johnmccabe/synapse,hankya/synapse,Yelp/synapse