fix #238 : add empty email check
fix #238 : add empty email check

ChangsungKim/TestRepository01,naver/yobi,brainagenet/yobi,ChangsungKim/TestRepository01,Limseunghwan/oss,naver/yobi,brainagenet/yobi,bloodybear/yona,yona-projects/yona,oolso/yobi,oolso/yobi,doortts/fork-yobi,violetag/demo,yona-projects/yona,naver/yobi,yona-projects/yona,Limseunghwan/oss,doortts/forked-for-history,oolso/yobi,ahb0327/yobi,doortts/fork-yobi,doortts/fork-yobi,ihoneymon/yobi,ihoneymon/yobi,bloodybear/yona,ahb0327/yobi,doortts/forked-for-history,ihoneymon/yobi,ahb0327/yobi,brainagenet/yobi,doortts/fork-yobi,yona-projects/yona,violetag/demo,bloodybear/yona,Limseunghwan/oss,doortts/forked-for-history,bloodybear/yona