Fast-path Linq Join on empty
Fast-path Linq Join on empty

If outer enumerable is empty, avoid creating Lookup<TKey, TInner>
(c.f. #5372).

If lookup is created but it is empty, short-circuit out of method.

zhenlan/corefx,MaggieTsang/corefx,gkhanna79/corefx,dotnet-bot/corefx,stone-li/corefx,ptoonen/corefx,dotnet-bot/corefx,alphonsekurian/corefx,Petermarcu/corefx,dsplaisted/corefx,rubo/corefx,Jiayili1/corefx,rahku/corefx,stone-li/corefx,stephenmichaelf/corefx,stephenmichaelf/corefx,gkhanna79/corefx,marksmeltzer/corefx,yizhang82/corefx,stone-li/corefx,kkurni/corefx,axelheer/corefx,pallavit/corefx,richlander/corefx,wtgodbe/corefx,shahid-pk/corefx,benpye/corefx,DnlHarvey/corefx,jlin177/corefx,SGuyGe/corefx,iamjasonp/corefx,stephenmichaelf/corefx,cydhaselton/corefx,YoupHulsebos/corefx,DnlHarvey/corefx,ptoonen/corefx,rahku/corefx,Jiayili1/corefx,lggomez/corefx,the-dwyer/corefx,wtgodbe/corefx,JosephTremoulet/corefx,lggomez/corefx,iamjasonp/corefx,benjamin-bader/corefx,tstringer/corefx,seanshpark/corefx,rahku/corefx,dhoehna/corefx,stone-li/corefx,ravimeda/corefx,Ermiar/corefx,cydhaselton/corefx,tijoytom/corefx,parjong/corefx,seanshpark/corefx,shahid-pk/corefx,dotnet-bot/corefx,jlin177/corefx,parjong/corefx,rubo/corefx,krk/corefx,richlander/corefx,gkhanna79/corefx,alphonsekurian/corefx,seanshpark/corefx,cartermp/corefx,dotnet-bot/corefx,cydhaselton/corefx,janhenke/corefx,ravimeda/corefx,DnlHarvey/corefx,yizhang82/corefx,alexperovich/corefx,krk/corefx,wtgodbe/corefx,shimingsg/corefx,fgreinacher/corefx,janhenke/corefx,adamralph/corefx,alphonsekurian/corefx,Priya91/corefx-1,cartermp/corefx,mazong1123/corefx,lggomez/corefx,mokchhya/corefx,krytarowski/corefx,mmitche/corefx,manu-silicon/corefx,jcme/corefx,jlin177/corefx,nchikanov/corefx,ptoonen/corefx,dsplaisted/corefx,weltkante/corefx,JosephTremoulet/corefx,the-dwyer/corefx,krk/corefx,jlin177/corefx,ericstj/corefx,Ermiar/corefx,ViktorHofer/corefx,MaggieTsang/corefx,seanshpark/corefx,Petermarcu/corefx,krytarowski/corefx,MaggieTsang/corefx,twsouthwick/corefx,ViktorHofer/corefx,Priya91/corefx-1,manu-silicon/corefx,alexperovich/corefx,adamralph/corefx,ericstj/corefx,ravimeda/corefx,iamjasonp/corefx,Petermarcu/corefx,marksmeltzer/corefx,nchikanov/corefx,cartermp/corefx,ptoonen/corefx,nbarbettini/corefx,yizhang82/corefx,SGuyGe/corefx,alphonsekurian/corefx,jhendrixMSFT/corefx,billwert/corefx,ViktorHofer/corefx,rjxby/corefx,shahid-pk/corefx,nchikanov/corefx,mazong1123/corefx,BrennanConroy/corefx,twsouthwick/corefx,manu-silicon/corefx,the-dwyer/corefx,alexperovich/corefx,manu-silicon/corefx,seanshpark/corefx,mmitche/corefx,dhoehna/corefx,twsouthwick/corefx,rahku/corefx,axelheer/corefx,tstringer/corefx,rahku/corefx,krytarowski/corefx,elijah6/corefx,lggomez/corefx,gkhanna79/corefx,manu-silicon/corefx,nchikanov/corefx,pallavit/corefx,shahid-pk/corefx,ellismg/corefx,Jiayili1/corefx,alexperovich/corefx,ericstj/corefx,krytarowski/corefx,marksmeltzer/corefx,gkhanna79/corefx,Priya91/corefx-1,billwert/corefx,wtgodbe/corefx,Chrisboh/corefx,benjamin-bader/corefx,ericstj/corefx,iamjasonp/corefx,Jiayili1/corefx,mokchhya/corefx,Ermiar/corefx,krytarowski/corefx,cartermp/corefx,zhenlan/corefx,jcme/corefx,axelheer/corefx,Priya91/corefx-1,gkhanna79/corefx,dhoehna/corefx,nbarbettini/corefx,JosephTremoulet/corefx,Ermiar/corefx,SGuyGe/corefx,Priya91/corefx-1,weltkante/corefx,zhenlan/corefx,fgreinacher/corefx,ravimeda/corefx,weltkante/corefx,marksmeltzer/corefx,yizhang82/corefx,rjxby/corefx,alphonsekurian/corefx,elijah6/corefx,nchikanov/corefx,tstringer/corefx,khdang/corefx,stephenmichaelf/corefx,jhendrixMSFT/corefx,shmao/corefx,seanshpark/corefx,cydhaselton/corefx,parjong/corefx,JosephTremoulet/corefx,ViktorHofer/corefx,ViktorHofer/corefx,Jiayili1/corefx,mokchhya/corefx,yizhang82/corefx,twsouthwick/corefx,YoupHulsebos/corefx,axelheer/corefx,nchikanov/corefx,mazong1123/corefx,Petermarcu/corefx,billwert/corefx,Jiayili1/corefx,rahku/corefx,kkurni/corefx,pallavit/corefx,SGuyGe/corefx,richlander/corefx,shmao/corefx,billwert/corefx,pallavit/corefx,stone-li/corefx,jcme/corefx,ViktorHofer/corefx,ericstj/corefx,tstringer/corefx,mmitche/corefx,billwert/corefx,axelheer/corefx,stone-li/corefx,elijah6/corefx,mazong1123/corefx,lggomez/corefx,alphonsekurian/corefx,manu-silicon/corefx,marksmeltzer/corefx,ellismg/corefx,rahku/corefx,cydhaselton/corefx,ravimeda/corefx,alexperovich/corefx,YoupHulsebos/corefx,ravimeda/corefx,dhoehna/corefx,Chrisboh/corefx,benpye/corefx,weltkante/corefx,dhoehna/corefx,wtgodbe/corefx,stephenmichaelf/corefx,mokchhya/corefx,nchikanov/corefx,elijah6/corefx,zhenlan/corefx,zhenlan/corefx,jhendrixMSFT/corefx,jlin177/corefx,shimingsg/corefx,twsouthwick/corefx,BrennanConroy/corefx,khdang/corefx,MaggieTsang/corefx,shahid-pk/corefx,richlander/corefx,stephenmichaelf/corefx,mazong1123/corefx,khdang/corefx,shimingsg/corefx,marksmeltzer/corefx,alexperovich/corefx,parjong/corefx,rubo/corefx,kkurni/corefx,dotnet-bot/corefx,alexperovich/corefx,iamjasonp/corefx,dotnet-bot/corefx,jlin177/corefx,shmao/corefx,ptoonen/corefx,rjxby/corefx,the-dwyer/corefx,cydhaselton/corefx,the-dwyer/corefx,tstringer/corefx,ViktorHofer/corefx,MaggieTsang/corefx,rjxby/corefx,krytarowski/corefx,shmao/corefx,jhendrixMSFT/corefx,elijah6/corefx,fgreinacher/corefx,nbarbettini/corefx,khdang/corefx,Ermiar/corefx,Chrisboh/corefx,ellismg/corefx,benpye/corefx,mmitche/corefx,rjxby/corefx,nbarbettini/corefx,MaggieTsang/corefx,DnlHarvey/corefx,benjamin-bader/corefx,benpye/corefx,weltkante/corefx,richlander/corefx,khdang/corefx,krk/corefx,Petermarcu/corefx,DnlHarvey/corefx,MaggieTsang/corefx,wtgodbe/corefx,ellismg/corefx,kkurni/corefx,jhendrixMSFT/corefx,adamralph/corefx,twsouthwick/corefx,iamjasonp/corefx,parjong/corefx,tijoytom/corefx,lggomez/corefx,mmitche/corefx,ptoonen/corefx,zhenlan/corefx,Ermiar/corefx,DnlHarvey/corefx,ravimeda/corefx,mazong1123/corefx,YoupHulsebos/corefx,stephenmichaelf/corefx,elijah6/corefx,richlander/corefx,mmitche/corefx,jhendrixMSFT/corefx,richlander/corefx,benjamin-bader/corefx,twsouthwick/corefx,shmao/corefx,shmao/corefx,lggomez/corefx,SGuyGe/corefx,Chrisboh/corefx,tstringer/corefx,JosephTremoulet/corefx,YoupHulsebos/corefx,janhenke/corefx,zhenlan/corefx,cartermp/corefx,dotnet-bot/corefx,shmao/corefx,Priya91/corefx-1,benjamin-bader/corefx,yizhang82/corefx,gkhanna79/corefx,manu-silicon/corefx,YoupHulsebos/corefx,marksmeltzer/corefx,Petermarcu/corefx,ptoonen/corefx,Ermiar/corefx,shimingsg/corefx,ellismg/corefx,jcme/corefx,tijoytom/corefx,axelheer/corefx,kkurni/corefx,nbarbettini/corefx,dhoehna/corefx,parjong/corefx,tijoytom/corefx,cydhaselton/corefx,rjxby/corefx,krk/corefx,the-dwyer/corefx,elijah6/corefx,shahid-pk/corefx,nbarbettini/corefx,khdang/corefx,krk/corefx,seanshpark/corefx,benjamin-bader/corefx,ellismg/corefx,rjxby/corefx,tijoytom/corefx,alphonsekurian/corefx,weltkante/corefx,krk/corefx,yizhang82/corefx,mokchhya/corefx,dsplaisted/corefx,mokchhya/corefx,wtgodbe/corefx,DnlHarvey/corefx,JosephTremoulet/corefx,benpye/corefx,janhenke/corefx,iamjasonp/corefx,ericstj/corefx,fgreinacher/corefx,pallavit/corefx,janhenke/corefx,mazong1123/corefx,billwert/corefx,Chrisboh/corefx,shimingsg/corefx,mmitche/corefx,Jiayili1/corefx,jlin177/corefx,kkurni/corefx,YoupHulsebos/corefx,weltkante/corefx,shimingsg/corefx,shimingsg/corefx,tijoytom/corefx,ericstj/corefx,rubo/corefx,janhenke/corefx,krytarowski/corefx,nbarbettini/corefx,tijoytom/corefx,the-dwyer/corefx,jcme/corefx,pallavit/corefx,rubo/corefx,Petermarcu/corefx,BrennanConroy/corefx,Chrisboh/corefx,parjong/corefx,jhendrixMSFT/corefx,benpye/corefx,jcme/corefx,stone-li/corefx,cartermp/corefx,billwert/corefx,dhoehna/corefx,JosephTremoulet/corefx,SGuyGe/corefx