store: define specific error for key not found.
store: define specific error for key not found.

It's needed when you want to know if the key exists.

wparad/rkt,tv42/rkt,lucasallan/rkt,rhvgoyal/rkt,blixtra/rkt,tv42/rkt,Yhgenomics/rkt,rkt/rkt,sinfomicien/rkt,dalanlan/rkt,shobhit85/rkt,alexhersh/rkt,tmrts/rkt,chrisseto/rkt,jonboulle/rkt,yifan-gu/rkt,MattDees/rkt,MattDees/rkt,maquanyi/rkt,xnox/rkt,achanda/rkt,blixtra/rkt,iankronquist/rkt,kinvolk/rkt,sgotti/rkt,rkt/rkt,rhvgoyal/rkt,rot26/rkt,achanda/rkt,joshix/rkt,kinvolk/rkt,krnowak/rkt,michelangelo13/rkt,ChengTiesheng/rkt,intelsdi-x/rkt,coreos/rkt,Wilybald/rkt,liugenping/rkt,tixxdz/rkt,tixxdz/rkt,il9ue/rkt,Shashwatsh/rkt,euank/rkt,crawford/rkt,jjlakis/rkt,nhlfr/rkt,liubq919/rkt,achanda/rkt,squaremo/rkt,shtouff/rkt,liubq919/rkt,Wilybald/rkt,rkt/rkt,adfernandes/rkt,intfrr/rkt,linki/rkt,kinvolk/rkt,tmrts/rkt,matthaias/rkt,adfernandes/rkt,euank/rkt,lee212/rkt,klizhentas/rkt,yifan-gu/rkt,akshaykarle/rkt,fdserr/rkt,Wilybald/rkt,kbrwn/rkt,alban/rkt,smarvin/rkt,cab105/rkt,sstabellini/rkt,rkt/rkt,cab105/rkt,bsmr-go/rkt,jasonchaffee/rkt,shobhit85/rkt,jasonchaffee/rkt,shobhit85/rkt,adfernandes/rkt,MabinGo/rkt,mattthias/pkg-rkt,clearlinux/rkt,clearlinux/rkt,sinfomicien/rkt,coreos/rkt,intelsdi-x/rkt,matthaias/rkt,jjlakis/rkt,linki/rkt,iaguis/rkt,endocode/rkt,luebken/rkt,kbrwn/rkt,michelangelo13/rkt,monstermunchkin/rkt,squeed/rkt,mike1729/rkt,squaremo/rkt,alban/rkt,ChengTiesheng/rkt,rot26/rkt,sstabellini/rkt,jonboulle/rkt,crawford/rkt,Wilybald/rkt,endocode/rkt,bsmr-go/rkt,alban/rkt,monstermunchkin/rkt,marineam/rkt,mjg59/rkt,yifan-gu/rocket,Shashwatsh/rkt,markllama/rkt,lee212/rkt,il9ue/rkt,tixxdz/rkt,coreos/rkt,liubq919/rkt,kbrwn/rkt,smarvin/rkt,xnox/rkt,jzelinskie/rkt,dalanlan/rkt,jakon89/rkt,chrisseto/rkt,jasonchaffee/rkt,MattDees/rkt,clearlinux/rkt,shtouff/rkt,matthaias/rkt,liugenping/rkt,intfrr/rkt,endocode/rkt,klizhentas/rkt,euank/rkt,sstabellini/rkt,s-urbaniak/rkt,MabinGo/rkt,lee212/rkt,dgonyeo/rkt,mike1729/rkt,blixtra/rkt,fdserr/rkt,lucasallan/rkt,dalanlan/rkt,markllama/rkt,akshaykarle/rkt,mattthias/pkg-rkt,krnowak/rkt,mjg59/rkt,maquanyi/rkt,tmrts/rkt,jzelinskie/rkt,alexhersh/rkt,liugenping/rkt,s-urbaniak/rkt,sinfomicien/rkt,michelangelo13/rkt,mike1729/rkt,klizhentas/rkt,marineam/rkt,squeed/rkt,linki/rkt,alexhersh/rkt,sgotti/rkt,bsmr-go/rkt,nhlfr/rkt,jjlakis/rkt,krnowak/rkt,akshaykarle/rkt,squaremo/rkt,kinvolk/rkt,ChengTiesheng/rkt,monstermunchkin/rkt,squeed/rkt,wparad/rkt,wparad/rkt,luebken/rkt,yifan-gu/rocket,yifan-gu/rkt,crawford/rkt,Shashwatsh/rkt,MabinGo/rkt,lucasallan/rkt,joshix/rkt,joshix/rkt,ybubnov/rkt,ybubnov/rkt,cab105/rkt,s-urbaniak/rkt,mattthias/pkg-rkt,nhlfr/rkt,jzelinskie/rkt,dgonyeo/rkt,Yhgenomics/rkt,rot26/rkt,jakon89/rkt,maquanyi/rkt,intelsdi-x/rkt,il9ue/rkt,luebken/rkt,dgonyeo/rkt,sgotti/rkt,shtouff/rkt,iankronquist/rkt,markllama/rkt,iaguis/rkt,ybubnov/rkt,marineam/rkt,Yhgenomics/rkt,iankronquist/rkt,fdserr/rkt,jakon89/rkt,xnox/rkt,smarvin/rkt,rhvgoyal/rkt,jonboulle/rkt,yifan-gu/rocket,tv42/rkt,joshix/rkt,chrisseto/rkt,mjg59/rkt,iaguis/rkt,lucasallan/rkt,intfrr/rkt