addGroup method Null safety
- CowGroup _
Implementation
void addGroup(CowGroup _) {
TextEditingController controller = TextEditingController()..text = _.name;
FocusNode focusNode = FocusNode();
controller.addListener(() => onChangeCowGroupName(_, controller.text));
_.controller = controller;
_.focusNode = focusNode;
_cowGroups.add(_);
notifyListeners();
}