private void appendMobMetadata(SetMultimap<TableName, String> mobRefSet) throws IOException {
      writer.appendFileInfo(MOB_FILE_REFS, MobUtils.serializeMobFileRefs(mobRefSet));
    }
Appends MOB - specific metadata (even if it is empty)
@param mobRefSet - original table -> set of MOB file names
@throws IOException problem writing to FS
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileWriter.java