code: public SyncToolConfig retrievePrevConfig(File backupDir) {
          File prevConfigBackupFile =
              new File(backupDir, PREV_BACKUP_FILE_NAME);
          if (prevConfigBackupFile.exists()) {
              String[] prevConfigArgs = retrieveConfig(prevConfigBackupFile);
              try {
                  return processStandardOptions(prevConfigArgs, false);
              } catch (ParseException e) {
                  return null;
              }
          } else {
              return null;
          }
      }
docs: Retrieves the configuration of the previous run of the Sync Tool.
  If there was no previous run, the backup file cannot be found, or
  the backup file cannot be read, returns null, otherwise returns the
  parsed configuration
  
  @param backupDir the current backup directory
  @return config for previous sync tool run, or null