public void removeUser(String username) {
    // TODO: handle if user doesn't exist!

    User removeUser = this.userStorage.remove(username);

    for (Mumble mumble : removeUser.getMumbles()) {
      this.mumbleStorage.remove(mumble.getId());
      this.mumbleTimeline.remove(mumble);
    }
  }
  public void removeMumble(String mumbleId) {
    // TODO: handle if mumble doesn't exist!

    Mumble removedMumble = this.mumbleStorage.remove(mumbleId);
    this.mumbleTimeline.remove(removedMumble);

    // remove the mumble from the User!
    User user = this.userStorage.get(removedMumble.getUsername());
    user.getMumbles().remove(removedMumble);
  }