stage1: don't set AC_METADATA_URL if it's empty
stage1: don't set AC_METADATA_URL if it's empty

yifan-gu/rocket,sinfomicien/rkt,jjlakis/rkt,endocode/rkt,shobhit85/rkt,liugenping/rkt,nhlfr/rkt,shobhit85/rkt,mike1729/rkt,linki/rkt,matthaias/rkt,ybubnov/rkt,tmrts/rkt,intelsdi-x/rkt,coreos/rkt,sstabellini/rkt,jjlakis/rkt,jonboulle/rkt,lucasallan/rkt,akshaykarle/rkt,monstermunchkin/rkt,jakon89/rkt,jasonchaffee/rkt,monstermunchkin/rkt,endocode/rkt,sgotti/rkt,euank/rkt,Wilybald/rkt,adfernandes/rkt,yifan-gu/rocket,markllama/rkt,nhlfr/rkt,liugenping/rkt,cab105/rkt,rkt/rkt,alban/rkt,matthaias/rkt,joshix/rkt,euank/rkt,il9ue/rkt,akshaykarle/rkt,yifan-gu/rocket,Shashwatsh/rkt,squeed/rkt,linki/rkt,achanda/rkt,Shashwatsh/rkt,jzelinskie/rkt,adfernandes/rkt,sstabellini/rkt,endocode/rkt,squeed/rkt,s-urbaniak/rkt,markllama/rkt,achanda/rkt,cab105/rkt,cab105/rkt,rkt/rkt,alban/rkt,nhlfr/rkt,jjlakis/rkt,alban/rkt,kinvolk/rkt,euank/rkt,rkt/rkt,liugenping/rkt,dgonyeo/rkt,kbrwn/rkt,yifan-gu/rkt,joshix/rkt,s-urbaniak/rkt,akshaykarle/rkt,kinvolk/rkt,sgotti/rkt,sgotti/rkt,blixtra/rkt,intelsdi-x/rkt,shobhit85/rkt,lucasallan/rkt,rkt/rkt,coreos/rkt,lucasallan/rkt,yifan-gu/rkt,ybubnov/rkt,dgonyeo/rkt,ybubnov/rkt,blixtra/rkt,joshix/rkt,mike1729/rkt,jakon89/rkt,markllama/rkt,kbrwn/rkt,kinvolk/rkt,jasonchaffee/rkt,dgonyeo/rkt,achanda/rkt,tmrts/rkt,blixtra/rkt,il9ue/rkt,squeed/rkt,jzelinskie/rkt,il9ue/rkt,coreos/rkt,sinfomicien/rkt,jakon89/rkt,Wilybald/rkt,krnowak/rkt,kbrwn/rkt,jonboulle/rkt,monstermunchkin/rkt,krnowak/rkt,jasonchaffee/rkt,joshix/rkt,matthaias/rkt,sinfomicien/rkt,jonboulle/rkt,tmrts/rkt,kinvolk/rkt,lucasallan/rkt,adfernandes/rkt,krnowak/rkt,yifan-gu/rkt,jzelinskie/rkt,mike1729/rkt,Wilybald/rkt,Shashwatsh/rkt,linki/rkt,intelsdi-x/rkt,sstabellini/rkt,Wilybald/rkt,s-urbaniak/rkt