private @Nullable Collection<@NotNull Node> getChildrenForWalker(@NotNull Node node, TreeWalkerBase<Node> walker, boolean allowLoading) {
    if (node.leafState == LeafState.ALWAYS || !allowLoading) return ContainerUtil.filter(node.getChildren(), Node::isLoaded);
    promiseChildren(node)
      .onSuccess(parent -> walker.setChildren(parent.getChildren()))
      .onError(walker::setError);
    return null;
  }
private @Nullable Collection<@NotNull Node> getChildrenForWalker(@NotNull Node node, TreeWalkerBase<Node> walker, boolean allowLoading)