skipTraversal property Null safety
This is sometimes useful if a Focus widget should receive key events as part of the focus chain, but shouldn't be accessible via focus traversal.
This is different from FocusNode.canRequestFocus because it only implies that the widget can't be reached via traversal, not that it can't be focused. It may still be focused explicitly.
bool get skipTraversal => _skipTraversal ?? focusNode?.skipTraversal ?? false;