fix error when preloading nested polymorphic association. Fix #539
fix error when preloading nested polymorphic association. Fix #539

sidaga/hummingbird,sidaga/hummingbird,xhocquet/hummingbird,vevix/hummingbird,sidaga/hummingbird,cybrox/hummingbird,qgustavor/hummingbird,saintsantos/hummingbird,xhocquet/hummingbird,vevix/hummingbird,MiLk/hummingbird,erengy/hummingbird,wlads/hummingbird,jcoady9/hummingbird,hummingbird-me/hummingbird,MiLk/hummingbird,vevix/hummingbird,qgustavor/hummingbird,Snitzle/hummingbird,astraldragon/hummingbird,Snitzle/hummingbird,astraldragon/hummingbird,xhocquet/hummingbird,qgustavor/hummingbird,erengy/hummingbird,saintsantos/hummingbird,saintsantos/hummingbird,paladique/hummingbird,paladique/hummingbird,hummingbird-me/hummingbird,xhocquet/hummingbird,jcoady9/hummingbird,synthtech/hummingbird,wlads/hummingbird,MiLk/hummingbird,synthtech/hummingbird,vevix/hummingbird,Snitzle/hummingbird,xhocquet/hummingbird,jcoady9/hummingbird,erengy/hummingbird,Snitzle/hummingbird,astraldragon/hummingbird,paladique/hummingbird,erengy/hummingbird,qgustavor/hummingbird,saintsantos/hummingbird,MiLk/hummingbird,xhocquet/hummingbird,wlads/hummingbird,wlads/hummingbird,paladique/hummingbird,astraldragon/hummingbird,xhocquet/hummingbird,sidaga/hummingbird,jcoady9/hummingbird