descendants property Null safety

Iterable<FocusNode> descendants

An Iterable over the hierarchy of children below this one, in depth-first order.

Implementation

Iterable<FocusNode> get descendants {
  if (_descendants == null) {
    final List<FocusNode> result = <FocusNode>[];
    for (final FocusNode child in _children) {
      result.addAll(child.descendants);
      result.add(child);
    }
    _descendants = result;
  }
  return _descendants!;
}