private void refreshAvailableUsers(List<User> users) {
   for (User user : users) {
     if (!group.getUsers().contains(user)) {
       fromUserStore.add(new UserData(user));
     }
   }
 }
  private void setFields() {
    nameTextBox.setValue(group.getName());
    for (User user : group.getUsers()) {
      toUserStore.add(new UserData(user));
    }

    loadAvailableUsers();
  }