code: @CommandArgument
    public void load(
        @OptionArgument("filename") String filename) {
  
      users.clear();
  
      try {
        BufferedReader reader = new BufferedReader(new FileReader(filename));
  
        while (reader.ready()) {
          User user = User.fromString(reader.readLine());
          users.put(user.username, user);
        }
      } catch (FileNotFoundException e) {
        System.err.println(String.format("File not found: '%s'", filename));
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
docs: Loads a users file.
  @param filename The filename of the users file to load.