docs: private static Tree findFootNode(Tree t) {
      Tree footNode = findFootNodeHelper(t);
      Tree result = footNode;
      if (footNode != null) {
        Tree parent = footNode.parent(t);
        int i = parent.indexOf(footNode);
        Tree newFootNode = footNode.treeFactory().newTreeNode(footNode.label(), new ArrayList<Tree>());
        parent.setChild(i, newFootNode);
        result = newFootNode;
      }
      return result;
    }