getGroup method
Implementation
(FGroup, AdditionalGroupConfigs) getGroup(int i) {
  final group = _getOnlyGroup(i);
  final additionalConfigs = AdditionalGroupConfigs(
    isEmpty: isGroupEmpty(group),
    correctedSpace: (groupLabelMaxSpace != null)
        ? (groupLabelMaxSpace! - _groupLabelSizes[i].getDim(directionNp))
        : 0.0,
  );
  return (group, additionalConfigs);
}