Fills in missing slots in transform data panels.
Fills in missing slots in transform data panels.

Forward fills data, so that when using multiple stocks,
we don't have cases where one stock has data and the other doesn't.

keir-rex/zipline,sketchytechky/zipline,michaeljohnbennett/zipline,jordancheah/zipline,davidastephens/zipline,gwulfs/zipline,keir-rex/zipline,magne-max/zipline-ja,cmorgan/zipline,jimgoo/zipline-fork,StratsOn/zipline,kmather73/zipline,wilsonkichoi/zipline,otmaneJai/Zipline,morrisonwudi/zipline,jordancheah/zipline,jimgoo/zipline-fork,grundgruen/zipline,morrisonwudi/zipline,MonoCloud/zipline,euri10/zipline,dhruvparamhans/zipline,CarterBain/AlephNull,humdings/zipline,joequant/zipline,ChinaQuants/zipline,magne-max/zipline-ja,stkubr/zipline,umuzungu/zipline,zhoulingjun/zipline,michaeljohnbennett/zipline,dmitriz/zipline,aajtodd/zipline,erikness/AlephOne,semio/zipline,ronalcc/zipline,ChinaQuants/zipline,erikness/AlephOne,StratsOn/zipline,zhoulingjun/zipline,otmaneJai/Zipline,MonoCloud/zipline,semio/zipline,wubr2000/zipline,humdings/zipline,chrjxj/zipline,cmorgan/zipline,joequant/zipline,umuzungu/zipline,kmather73/zipline,wilsonkichoi/zipline,florentchandelier/zipline,CDSFinance/zipline,dkushner/zipline,davidastephens/zipline,iamkingmaker/zipline,grundgruen/zipline,CDSFinance/zipline,sketchytechky/zipline,quantopian/zipline,nborggren/zipline,dmitriz/zipline,florentchandelier/zipline,Scapogo/zipline,aajtodd/zipline,wubr2000/zipline,AlirezaShahabi/zipline,alphaBenj/zipline,bartosh/zipline,enigmampc/catalyst,chrjxj/zipline,AlirezaShahabi/zipline,stkubr/zipline,quantopian/zipline,YuepengGuo/zipline,mattcaldwell/zipline,CarterBain/AlephNull,ronalcc/zipline,bartosh/zipline,alphaBenj/zipline,dkushner/zipline,DVegaCapital/zipline,Scapogo/zipline,enigmampc/catalyst,dhruvparamhans/zipline,nborggren/zipline,gwulfs/zipline,iamkingmaker/zipline,mattcaldwell/zipline,DVegaCapital/zipline,YuepengGuo/zipline,euri10/zipline