Fixed error with Cart promotion handler when line_item was nil
Fixed error with Cart promotion handler when line_item was nil

Fixes #3931

tesserakt/clean_spree,jparr/spree,rajeevriitm/spree,groundctrl/spree,beni55/spree,jeffboulet/spree,mindvolt/spree,tailic/spree,moneyspyder/spree,keatonrow/spree,dandanwei/spree,TrialGuides/spree,alejandromangione/spree,zaeznet/spree,Arpsara/solidus,gautamsawhney/spree,brchristian/spree,watg/spree,jimblesm/spree,raow/spree,CiscoCloud/spree,net2b/spree,imella/spree,grzlus/solidus,Boomkat/spree,caiqinghua/spree,njerrywerry/spree,hoanghiep90/spree,ujai/spree,grzlus/spree,AgilTec/spree,DarkoP/spree,KMikhaylovCTG/spree,patdec/spree,Nevensoft/spree,DarkoP/spree,berkes/spree,hifly/spree,alvinjean/spree,vinsol/spree,beni55/spree,karlitxo/spree,CiscoCloud/spree,kewaunited/spree,RatioClothing/spree,ahmetabdi/spree,jasonfb/spree,grzlus/solidus,degica/spree,welitonfreitas/spree,Ropeney/spree,patdec/spree,tailic/spree,pervino/solidus,FadliKun/spree,yiqing95/spree,patdec/spree,caiqinghua/spree,robodisco/spree,TrialGuides/spree,shaywood2/spree,ramkumar-kr/spree,jspizziri/spree,keatonrow/spree,azranel/spree,Arpsara/solidus,hifly/spree,abhishekjain16/spree,zaeznet/spree,siddharth28/spree,dafontaine/spree,lyzxsc/spree,wolfieorama/spree,berkes/spree,Kagetsuki/spree,berkes/spree,sfcgeorge/spree,thogg4/spree,kewaunited/spree,derekluo/spree,StemboltHQ/spree,volpejoaquin/spree,KMikhaylovCTG/spree,APohio/spree,Mayvenn/spree,carlesjove/spree,pervino/solidus,TrialGuides/spree,pulkit21/spree,jeffboulet/spree,grzlus/spree,gregoryrikson/spree-sample,jaspreet21anand/spree,reinaris/spree,Engeltj/spree,bjornlinder/Spree,pervino/solidus,beni55/spree,vinayvinsol/spree,agient/agientstorefront,radarseesradar/spree,ahmetabdi/spree,Lostmyname/spree,groundctrl/spree,jeffboulet/spree,forkata/solidus,calvinl/spree,adaddeo/spree,joanblake/spree,Boomkat/spree,FadliKun/spree,ahmetabdi/spree,Kagetsuki/spree,jordan-brough/solidus,forkata/solidus,jeffboulet/spree,pjmj777/spree,yiqing95/spree,mleglise/spree,piousbox/spree,alepore/spree,hoanghiep90/spree,freerunningtech/spree,JuandGirald/spree,FadliKun/spree,dafontaine/spree,radarseesradar/spree,alvinjean/spree,wolfieorama/spree,rbngzlv/spree,sliaquat/spree,biagidp/spree,jimblesm/spree,JDutil/spree,mindvolt/spree,omarsar/spree,priyank-gupta/spree,ahmetabdi/spree,orenf/spree,pervino/solidus,vmatekole/spree,assembledbrands/spree,shaywood2/spree,dandanwei/spree,net2b/spree,trigrass2/spree,kewaunited/spree,vmatekole/spree,PhoenixTeam/spree_phoenix,softr8/spree,welitonfreitas/spree,softr8/spree,tancnle/spree,odk211/spree,bonobos/solidus,shioyama/spree,builtbybuffalo/spree,APohio/spree,welitonfreitas/spree,sliaquat/spree,adaddeo/spree,shekibobo/spree,vcavallo/spree,useiichi/spree,rajeevriitm/spree,imella/spree,softr8/spree,PhoenixTeam/spree_phoenix,jimblesm/spree,RatioClothing/spree,shaywood2/spree,jaspreet21anand/spree,project-eutopia/spree,Machpowersystems/spree_mach,zamiang/spree,camelmasa/spree,nooysters/spree,jsurdilla/solidus,calvinl/spree,abhishekjain16/spree,delphsoft/spree-store-ballchair,Engeltj/spree,TimurTarasenko/spree,tesserakt/clean_spree,Boomkat/spree,reidblomquist/spree,alvinjean/spree,maybii/spree,Senjai/spree,alvinjean/spree,yomishra/pce,net2b/spree,vulk/spree,devilcoders/solidus,yiqing95/spree,reidblomquist/spree,Lostmyname/spree,omarsar/spree,derekluo/spree,robodisco/spree,yiqing95/spree,vmatekole/spree,JDutil/spree,progsri/spree,Senjai/solidus,sunny2601/spree,Mayvenn/spree,jsurdilla/solidus,shioyama/spree,JDutil/spree,moneyspyder/spree,miyazawatomoka/spree,pjmj777/spree,SadTreeFriends/spree,ayb/spree,CiscoCloud/spree,Kagetsuki/spree,ayb/spree,carlesjove/spree,delphsoft/spree-store-ballchair,maybii/spree,biagidp/spree,jasonfb/spree,sfcgeorge/spree,camelmasa/spree,tancnle/spree,thogg4/spree,pervino/spree,StemboltHQ/spree,raow/spree,vinsol/spree,orenf/spree,pulkit21/spree,joanblake/spree,gautamsawhney/spree,forkata/solidus,keatonrow/spree,groundctrl/spree,Hawaiideveloper/shoppingcart,softr8/spree,rbngzlv/spree,robodisco/spree,moneyspyder/spree,rajeevriitm/spree,volpejoaquin/spree,Migweld/spree,carlesjove/spree,SadTreeFriends/spree,robodisco/spree,assembledbrands/spree,reinaris/spree,edgward/spree,ckk-scratch/solidus,jasonfb/spree,rakibulislam/spree,bricesanchez/spree,Engeltj/spree,wolfieorama/spree,camelmasa/spree,pulkit21/spree,agient/agientstorefront,TrialGuides/spree,locomotivapro/spree,firman/spree,athal7/solidus,Senjai/solidus,quentinuys/spree,delphsoft/spree-store-ballchair,hoanghiep90/spree,azclick/spree,watg/spree,jspizziri/spree,scottcrawford03/solidus,brchristian/spree,reinaris/spree,abhishekjain16/spree,useiichi/spree,zamiang/spree,welitonfreitas/spree,woboinc/spree,builtbybuffalo/spree,azranel/spree,fahidnasir/spree,LBRapid/spree,richardnuno/solidus,ujai/spree,scottcrawford03/solidus,wolfieorama/spree,karlitxo/spree,xuewenfei/solidus,Hates/spree,lsirivong/solidus,biagidp/spree,njerrywerry/spree,zamiang/spree,Senjai/spree,alejandromangione/spree,ramkumar-kr/spree,dafontaine/spree,ckk-scratch/solidus,miyazawatomoka/spree,degica/spree,Ropeney/spree,bricesanchez/spree,trigrass2/spree,joanblake/spree,agient/agientstorefront,PhoenixTeam/spree_phoenix,cutefrank/spree,surfdome/spree,archSeer/spree,vulk/spree,degica/spree,dafontaine/spree,ramkumar-kr/spree,scottcrawford03/solidus,jsurdilla/solidus,vulk/spree,CJMrozek/spree,Arpsara/solidus,sideci-sample/sideci-sample-spree,FadliKun/spree,vulk/spree,njerrywerry/spree,Migweld/spree,shekibobo/spree,tancnle/spree,alepore/spree,dandanwei/spree,rbngzlv/spree,progsri/spree,NerdsvilleCEO/spree,groundctrl/spree,SadTreeFriends/spree,cutefrank/spree,Engeltj/spree,xuewenfei/solidus,yushine/spree,kewaunited/spree,Machpowersystems/spree_mach,madetech/spree,shekibobo/spree,miyazawatomoka/spree,rakibulislam/spree,CiscoCloud/spree,xuewenfei/solidus,hoanghiep90/spree,builtbybuffalo/spree,miyazawatomoka/spree,yomishra/pce,knuepwebdev/FloatTubeRodHolders,quentinuys/spree,adaddeo/spree,surfdome/spree,athal7/solidus,priyank-gupta/spree,hifly/spree,sliaquat/spree,karlitxo/spree,pervino/spree,useiichi/spree,yushine/spree,madetech/spree,useiichi/spree,lyzxsc/spree,freerunningtech/spree,yushine/spree,firman/spree,jasonfb/spree,tesserakt/clean_spree,LBRapid/spree,mleglise/spree,rajeevriitm/spree,archSeer/spree,JuandGirald/spree,pjmj777/spree,brchristian/spree,radarseesradar/spree,edgward/spree,assembledbrands/spree,woboinc/spree,shioyama/spree,keatonrow/spree,caiqinghua/spree,trigrass2/spree,mleglise/spree,CJMrozek/spree,njerrywerry/spree,surfdome/spree,jspizziri/spree,lyzxsc/spree,odk211/spree,jordan-brough/solidus,project-eutopia/spree,nooysters/spree,bonobos/solidus,siddharth28/spree,athal7/solidus,carlesjove/spree,madetech/spree,jparr/spree,dotandbo/spree,Senjai/spree,lsirivong/solidus,grzlus/solidus,jordan-brough/solidus,Hawaiideveloper/shoppingcart,lsirivong/solidus,alepore/spree,mindvolt/spree,gautamsawhney/spree,reidblomquist/spree,knuepwebdev/FloatTubeRodHolders,maybii/spree,volpejoaquin/spree,dotandbo/spree,omarsar/spree,NerdsvilleCEO/spree,DynamoMTL/spree,Senjai/solidus,reidblomquist/spree,bjornlinder/Spree,thogg4/spree,devilcoders/solidus,AgilTec/spree,TimurTarasenko/spree,gregoryrikson/spree-sample,edgward/spree,vinsol/spree,fahidnasir/spree,bjornlinder/Spree,project-eutopia/spree,AgilTec/spree,rakibulislam/spree,odk211/spree,pervino/spree,DynamoMTL/spree,Mayvenn/spree,raow/spree,gregoryrikson/spree-sample,pulkit21/spree,vcavallo/spree,zaeznet/spree,sunny2601/spree,Mayvenn/spree,mleglise/spree,progsri/spree,lsirivong/spree,karlitxo/spree,progsri/spree,vcavallo/spree,project-eutopia/spree,piousbox/spree,rbngzlv/spree,Hates/spree,sfcgeorge/spree,jordan-brough/solidus,CJMrozek/spree,omarsar/spree,vcavallo/spree,alejandromangione/spree,tancnle/spree,calvinl/spree,AgilTec/spree,tomash/spree,woboinc/spree,agient/agientstorefront,imella/spree,zaeznet/spree,jimblesm/spree,Hawaiideveloper/shoppingcart,ujai/spree,vinayvinsol/spree,richardnuno/solidus,CJMrozek/spree,archSeer/spree,Lostmyname/spree,patdec/spree,grzlus/spree,RatioClothing/spree,locomotivapro/spree,Machpowersystems/spree_mach,builtbybuffalo/spree,orenf/spree,nooysters/spree,PhoenixTeam/spree_phoenix,sfcgeorge/spree,vinayvinsol/spree,DynamoMTL/spree,knuepwebdev/FloatTubeRodHolders,TimurTarasenko/spree,jsurdilla/solidus,radarseesradar/spree,locomotivapro/spree,DynamoMTL/spree,Ropeney/spree,xuewenfei/solidus,Nevensoft/spree,Ropeney/spree,yomishra/pce,grzlus/spree,tomash/spree,piousbox/spree,bonobos/solidus,jparr/spree,gregoryrikson/spree-sample,orenf/spree,JDutil/spree,azclick/spree,lsirivong/solidus,shaywood2/spree,KMikhaylovCTG/spree,vinayvinsol/spree,trigrass2/spree,edgward/spree,derekluo/spree,cutefrank/spree,devilcoders/solidus,dotandbo/spree,tesserakt/clean_spree,watg/spree,dandanwei/spree,DarkoP/spree,Migweld/spree,piousbox/spree,athal7/solidus,Hawaiideveloper/shoppingcart,Hates/spree,fahidnasir/spree,dotandbo/spree,azranel/spree,siddharth28/spree,priyank-gupta/spree,volpejoaquin/spree,pervino/spree,NerdsvilleCEO/spree,adaddeo/spree,hifly/spree,lyzxsc/spree,joanblake/spree,sunny2601/spree,delphsoft/spree-store-ballchair,jspizziri/spree,bricesanchez/spree,NerdsvilleCEO/spree,tomash/spree,jordan-brough/spree,rakibulislam/spree,ckk-scratch/solidus,JuandGirald/spree,moneyspyder/spree,sliaquat/spree,mindvolt/spree,jaspreet21anand/spree,forkata/solidus,StemboltHQ/spree,azclick/spree,surfdome/spree,cutefrank/spree,lsirivong/spree,lsirivong/spree,bonobos/solidus,lsirivong/spree,net2b/spree,yushine/spree,grzlus/solidus,firman/spree,Senjai/solidus,tailic/spree,sunny2601/spree,JuandGirald/spree,SadTreeFriends/spree,beni55/spree,locomotivapro/spree,ayb/spree,quentinuys/spree,Migweld/spree,APohio/spree,ckk-scratch/solidus,camelmasa/spree,Boomkat/spree,firman/spree,Arpsara/solidus,abhishekjain16/spree,maybii/spree,siddharth28/spree,priyank-gupta/spree,freerunningtech/spree,ramkumar-kr/spree,Hates/spree,DarkoP/spree,richardnuno/solidus,Nevensoft/spree,richardnuno/solidus,shekibobo/spree,Nevensoft/spree,KMikhaylovCTG/spree,scottcrawford03/solidus,APohio/spree,reinaris/spree,nooysters/spree,berkes/spree,azclick/spree,ayb/spree,vmatekole/spree,fahidnasir/spree,Kagetsuki/spree,azranel/spree,Lostmyname/spree,alejandromangione/spree,jordan-brough/spree,vinsol/spree,devilcoders/solidus,thogg4/spree,jaspreet21anand/spree,LBRapid/spree,odk211/spree,madetech/spree,sideci-sample/sideci-sample-spree,zamiang/spree,archSeer/spree,brchristian/spree,TimurTarasenko/spree,gautamsawhney/spree,raow/spree,calvinl/spree,jordan-brough/spree,jparr/spree,caiqinghua/spree,sideci-sample/sideci-sample-spree,quentinuys/spree,derekluo/spree,tomash/spree