modelProperty doesn't need to check for null
modelProperty doesn't need to check for null

Since `#models` is filled with only model instances, there's no need to
check if model isn't `null`.

re: #3667.

mrblueblue/backbone,Connectlegendary/backbone,jashkenas/backbone,embarknow/backbone,zgl2007dj/backbone,jungjung917/backbone,zhangwei001/backbone,wangdahoo/backbone,craigmichaelmartin/backbone,fanhc019/backbone,nikolas/backbone,vincent1988/backbone,ThiagoGarciaAlves/backbone,huanglp47/backbone,alekskorolev/lightbones,guahanweb/backbone,anhtholee/backbone,jewsroch/backbone,dak/backbone,sumyfly/backbone,akre54/backbone,gougouGet/backbone,ntgn81/backbone,wangcan2014/backbone,lujocom/backbone,getshuvo/backbone,GrimDerp/backbone,linalu1/backbone,rashmisajjan/backbone,paulfalgout/backbone,chyeh727/backbone,tadwhitaker/backbone,Niades/backbone,premkumargithub/backbone,elancom/backbone,wushuyi/backbone,closeio/backbone,trizko/backbone,ThiagoGarciaAlves/backbone,moccen/backbone,sumyfly/backbone,sunday-star/backbone,sunday-star/backbone,wushuyi/backbone,Sachin-Ganesh/backbone,zhangdimelody/backbone,moimikey/backbone,jungjung917/backbone,pandoraui/backbone,DannyDelott/backbone,darrrk/backbone,lastjune/backbone,ohbarye/backbone,timebackzhou/backbone,tzkKrbys/backbone,akre54/backbone,premkumargithub/backbone,sitexa/backbone,ridixcr/backbone,Bug2014/backbone,fanhc019/backbone,Sachin-Ganesh/backbone,howtolearntocode/backbone,rashmisajjan/backbone,DannyDelott/backbone,neocotic/hipbone,zgl2007dj/backbone,zhoufan879/backbone,ywenjinlin/backbone,vin100bk/backbone,gougouGet/backbone,au-phiware/backbone,lastjune/backbone,Flip120/backbone,moimikey/backbone,elma-cao/backbone,dcheepurupalli/backbone,feychenie/backbone,chyeh727/backbone,getshuvo/backbone,tibic/backbone,udhayam/backbone,yuhualingfeng/backbone,au-phiware/backbone,craigmichaelmartin/backbone,ohbarye/backbone,yawenl/backbone,elancom/backbone,jashkenas/backbone,lujocom/backbone,sueyeh/backbone,elma-cao/backbone,huanglp47/backbone,FishbaitHarry/backbone,mrblueblue/backbone,jridgewell/backbone,Diwahars/backbone,cgvarela/backbone,paulfalgout/backbone,aihua/backbone,Krasnyanskiy/backbone,pandoraui/backbone,tibic/backbone,liudianpeng/backbone,timebackzhou/backbone,aihua/backbone,sueyeh/backbone,sitexa/backbone,udhayam/backbone,platinumazure/backbone,Diwahars/backbone,dak/backbone,linalu1/backbone,leimd/backbone,yuhualingfeng/backbone,wjb12/backbone,vincent1988/backbone,leimd/backbone,nikolas/backbone,zdespolit/backbone,Niades/backbone,tzkKrbys/backbone,wxmfront/backbone,neocotic/hipbone,wangcan2014/backbone,7213/backbone,wxmfront/backbone,GrimDerp/backbone,trizko/backbone,cgvarela/backbone,ywenjinlin/backbone,jridgewell/backbone,yawenl/backbone,closeio/backbone,feychenie/backbone,howtolearntocode/backbone,guahanweb/backbone,Connectlegendary/backbone,streamablevideo/backbone,heroazure/backbone,zhangwei001/backbone,ntgn81/backbone,zhoufan879/backbone,zdespolit/backbone,youprofit/backbone,darrrk/backbone,wangdahoo/backbone,ppker/backbone,streamablevideo/backbone,heroazure/backbone,ppker/backbone,ridixcr/backbone,alekskorolev/lightbones,Krasnyanskiy/backbone,youprofit/backbone,platinumazure/backbone,7213/backbone,anhtholee/backbone,liudianpeng/backbone,embarknow/backbone,Bug2014/backbone,FishbaitHarry/backbone,Flip120/backbone,wjb12/backbone,dcheepurupalli/backbone,tadwhitaker/backbone,jewsroch/backbone,vin100bk/backbone,zhangdimelody/backbone,moccen/backbone