docs: public Date getLastBackupTime() {
  		long time = System.currentTimeMillis();
  		String lastBackupTime = redis.getSet(KEY, Long.toString(time));
  		if (lastBackupTime == null || lastBackupTime.length() == 0) {
  			return null;
  		}
  		long backupTime = Long.parseLong(lastBackupTime);
  		if (backupTime <= 0) {
  			return null;
  		}
  		return new Date(backupTime);
  	}