append '{}' for the log when props is missing
append '{}' for the log when props is missing

additionally, avoid that commitConsumerOffset runs
at the same time with saveAsTextFile

SteamShon/incubator-s2graph,daewon/incubator-s2graph,SteamShon/incubator-s2graph,daewon/incubator-s2graph,SteamShon/incubator-s2graph,jongwook/incubator-s2graph,jongwook/incubator-s2graph