core: fix exception when checksum type is nil
core: fix exception when checksum type is nil

Thanks @johnbellone

philwrenn/vagrant,clinstid/vagrant,jberends/vagrant,gbarberi/vagrant,wangfakang/vagrant,invernizzi-at-google/vagrant,bryson/vagrant,Endika/vagrant,Endika/vagrant,ianmiell/vagrant,gajdaw/vagrant,shtouff/vagrant,kamigerami/vagrant,mkuzmin/vagrant,iNecas/vagrant,vamegh/vagrant,Sgoettschkes/vagrant,johntron/vagrant,mwarren/vagrant,jhoblitt/vagrant,Ninir/vagrant,apertoso/vagrant,dharmab/vagrant,nickryand/vagrant,carlosefr/vagrant,bheuvel/vagrant,taliesins/vagrant,marxarelli/vagrant,jean/vagrant,bheuvel/vagrant,jtopper/vagrant,kamazee/vagrant,kamazee/vagrant,loren-osborn/vagrant,wangfakang/vagrant,Chhunlong/vagrant,gitebra/vagrant,jmanero/vagrant,fnewberg/vagrant,Avira/vagrant,Sgoettschkes/vagrant,sferik/vagrant,MiLk/vagrant,tbarrongh/vagrant,crashlytics/vagrant,teotihuacanada/vagrant,tknerr/vagrant,gajdaw/vagrant,doy/vagrant,sax/vagrant,mpoeter/vagrant,p0deje/vagrant,mwarren/vagrant,shtouff/vagrant,ArloL/vagrant,philwrenn/vagrant,mwrock/vagrant,Chhed13/vagrant,nickryand/vagrant,tjanez/vagrant,mwrock/vagrant,miguel250/vagrant,signed8bit/vagrant,tomfanning/vagrant,jfchevrette/vagrant,h4ck3rm1k3/vagrant,aaam/vagrant,lukebakken/vagrant,juiceinc/vagrant,h4ck3rm1k3/vagrant,dhoer/vagrant,tknerr/vagrant,blueyed/vagrant,kamazee/vagrant,bryson/vagrant,cgvarela/vagrant,patrys/vagrant,obnoxxx/vagrant,sni/vagrant,kalabiyau/vagrant,gitebra/vagrant,sideci-sample/sideci-sample-vagrant,modulexcite/vagrant,dhoer/vagrant,zsjohny/vagrant,Chhunlong/vagrant,denisbr/vagrant,wkolean/vagrant,darkn3rd/vagrant,marxarelli/vagrant,stephancom/vagrant,tjanez/vagrant,jean/vagrant,gpkfr/vagrant,tbarrongh/vagrant,jtopper/vagrant,bshurts/vagrant,jean/vagrant,tschortsch/vagrant,vamegh/vagrant,bshurts/vagrant,dharmab/vagrant,jmanero/vagrant,pwnall/vagrant,invernizzi-at-google/vagrant,aneeshusa/vagrant,tomfanning/vagrant,marxarelli/vagrant,mwrock/vagrant,denisbr/vagrant,mkuzmin/vagrant,bheuvel/vagrant,lukebakken/vagrant,kalabiyau/vagrant,chrisvire/vagrant,jkburges/vagrant,BlakeMesdag/vagrant,cgvarela/vagrant,sni/vagrant,dustymabe/vagrant,Chhed13/vagrant,teotihuacanada/vagrant,Sgoettschkes/vagrant,modulexcite/vagrant,Chhunlong/vagrant,gbarberi/vagrant,obnoxxx/vagrant,gbarberi/vagrant,chrisvire/vagrant,ianmiell/vagrant,zsjohny/vagrant,dharmab/vagrant,bshurts/vagrant,taliesins/vagrant,janek-warchol/vagrant,sax/vagrant,mkuzmin/vagrant,justincampbell/vagrant,pwnall/vagrant,philoserf/vagrant,lukebakken/vagrant,benizi/vagrant,aaam/vagrant,jkburges/vagrant,tbriggs-curse/vagrant,TheBigBear/vagrant,bdwyertech/vagrant,ferventcoder/vagrant,teotihuacanada/vagrant,miguel250/vagrant,blueyed/vagrant,myrjola/vagrant,fnewberg/vagrant,benh57/vagrant,legal90/vagrant,rivy/vagrant,channui/vagrant,evverx/vagrant,invernizzi-at-google/vagrant,benizi/vagrant,MiLk/vagrant,muhanadra/vagrant,carlosefr/vagrant,mpoeter/vagrant,jfchevrette/vagrant,gpkfr/vagrant,teotihuacanada/vagrant,pwnall/vagrant,janek-warchol/vagrant,cgvarela/vagrant,dharmab/vagrant,krig/vagrant,senglin/vagrant,tomfanning/vagrant,PatOShea/vagrant,shtouff/vagrant,tschortsch/vagrant,lonniev/vagrant,lonniev/vagrant,wangfakang/vagrant,vamegh/vagrant,jfchevrette/vagrant,fnewberg/vagrant,lukebakken/vagrant,Endika/vagrant,bshurts/vagrant,loren-osborn/vagrant,bdwyertech/vagrant,jtopper/vagrant,ferventcoder/vagrant,PatOShea/vagrant,chrisroberts/vagrant,johntron/vagrant,crashlytics/vagrant,modulexcite/vagrant,philoserf/vagrant,signed8bit/vagrant,janek-warchol/vagrant,tbriggs-curse/vagrant,Avira/vagrant,tomfanning/vagrant,genome21/vagrant,stephancom/vagrant,fnewberg/vagrant,TheBigBear/vagrant,tbarrongh/vagrant,Ninir/vagrant,Avira/vagrant,MiLk/vagrant,chrisroberts/vagrant,lonniev/vagrant,wkolean/vagrant,sideci-sample/sideci-sample-vagrant,justincampbell/vagrant,obnoxxx/vagrant,petems/vagrant,h4ck3rm1k3/vagrant,philwrenn/vagrant,chrisroberts/vagrant,apertoso/vagrant,darkn3rd/vagrant,tbarrongh/vagrant,Chhed13/vagrant,krig/vagrant,PatrickLang/vagrant,shtouff/vagrant,iNecas/vagrant,genome21/vagrant,kamigerami/vagrant,mkuzmin/vagrant,myrjola/vagrant,mpoeter/vagrant,channui/vagrant,stephancom/vagrant,petems/vagrant,patrys/vagrant,miguel250/vagrant,gitebra/vagrant,dhoer/vagrant,h4ck3rm1k3/vagrant,gbarberi/vagrant,bdwyertech/vagrant,evverx/vagrant,doy/vagrant,gajdaw/vagrant,myrjola/vagrant,sferik/vagrant,benizi/vagrant,tbriggs-curse/vagrant,petems/vagrant,channui/vagrant,krig/vagrant,aneeshusa/vagrant,jmanero/vagrant,clinstid/vagrant,dustymabe/vagrant,johntron/vagrant,TheBigBear/vagrant,wangfakang/vagrant,signed8bit/vagrant,blueyed/vagrant,zsjohny/vagrant,otagi/vagrant,TheBigBear/vagrant,marxarelli/vagrant,doy/vagrant,crashlytics/vagrant,tjanez/vagrant,signed8bit/vagrant,clinstid/vagrant,otagi/vagrant,crashlytics/vagrant,sax/vagrant,jkburges/vagrant,jberends/vagrant,kamazee/vagrant,theist/vagrant,iNecas/vagrant,Ninir/vagrant,jhoblitt/vagrant,ianmiell/vagrant,ArloL/vagrant,pwnall/vagrant,jberends/vagrant,wkolean/vagrant,invernizzi-at-google/vagrant,nickryand/vagrant,gitebra/vagrant,ferventcoder/vagrant,jhoblitt/vagrant,jmanero/vagrant,kalabiyau/vagrant,bheuvel/vagrant,otagi/vagrant,muhanadra/vagrant,doy/vagrant,apertoso/vagrant,tknerr/vagrant,justincampbell/vagrant,juiceinc/vagrant,evverx/vagrant,jkburges/vagrant,taliesins/vagrant,senglin/vagrant,nickryand/vagrant,aaam/vagrant,aaam/vagrant,denisbr/vagrant,mwarren/vagrant,vamegh/vagrant,theist/vagrant,bdwyertech/vagrant,blueyed/vagrant,rivy/vagrant,genome21/vagrant,darkn3rd/vagrant,muhanadra/vagrant,stephancom/vagrant,tschortsch/vagrant,loren-osborn/vagrant,sferik/vagrant,PatrickLang/vagrant,juiceinc/vagrant,johntron/vagrant,petems/vagrant,mwrock/vagrant,senglin/vagrant,tjanez/vagrant,jtopper/vagrant,taliesins/vagrant,justincampbell/vagrant,benizi/vagrant,chrisvire/vagrant,apertoso/vagrant,legal90/vagrant,modulexcite/vagrant,lonniev/vagrant,sideci-sample/sideci-sample-vagrant,tschortsch/vagrant,genome21/vagrant,patrys/vagrant,jhoblitt/vagrant,mwarren/vagrant,dhoer/vagrant,mitchellh/vagrant,philwrenn/vagrant,juiceinc/vagrant,otagi/vagrant,Chhunlong/vagrant,benh57/vagrant,gpkfr/vagrant,kamigerami/vagrant,PatOShea/vagrant,darkn3rd/vagrant,ArloL/vagrant,PatrickLang/vagrant,Sgoettschkes/vagrant,carlosefr/vagrant,denisbr/vagrant,p0deje/vagrant,BlakeMesdag/vagrant,dustymabe/vagrant,p0deje/vagrant,Chhed13/vagrant,miguel250/vagrant,benh57/vagrant,mitchellh/vagrant,sax/vagrant,theist/vagrant,Avira/vagrant,patrys/vagrant,bryson/vagrant,ferventcoder/vagrant,legal90/vagrant,BlakeMesdag/vagrant,PatrickLang/vagrant,janek-warchol/vagrant,chrisvire/vagrant,legal90/vagrant,sni/vagrant,myrjola/vagrant,bryson/vagrant,chrisroberts/vagrant,wkolean/vagrant,tknerr/vagrant,carlosefr/vagrant,benh57/vagrant,dustymabe/vagrant,senglin/vagrant,philoserf/vagrant,PatOShea/vagrant,theist/vagrant,mpoeter/vagrant,mitchellh/vagrant,aneeshusa/vagrant,aneeshusa/vagrant,zsjohny/vagrant,kalabiyau/vagrant,philoserf/vagrant,muhanadra/vagrant,ArloL/vagrant,jean/vagrant,Endika/vagrant,jberends/vagrant,loren-osborn/vagrant,sni/vagrant,ianmiell/vagrant,rivy/vagrant,jfchevrette/vagrant,mitchellh/vagrant,kamigerami/vagrant,gpkfr/vagrant,krig/vagrant,tbriggs-curse/vagrant,cgvarela/vagrant,rivy/vagrant