docs: protected void cleanOutOldAvatars(File directory, int maxLifeInDays){
          if (directory != null){
              if (mCleanedDirectories.contains(directory.getAbsolutePath())){
                  return;
              }
              long oldestTimeAllowed = System.currentTimeMillis() - maxLifeInDays * TimeUnit.DAYS.toMillis(maxLifeInDays);
              File[] files = directory.listFiles();
              if (files != null){
                  for (File file : files){
                      if (file.getName().startsWith(DEFAULT_AVATAR_FILE_PREFIX) && file.lastModified() < oldestTimeAllowed){
                          file.delete();
                      }
                  }
              }
          }
      }