private @NotNull <T extends UserDataHolder> ECollection addWeaklyTrackedEmptyStack(@NotNull T holder, @NotNull Collection<? super T> allHolders) {
    ECollection result = holder.getUserData(STACK_IN_DOCUMENT_KEY);
    if (result == null) {
      holder.putUserData(STACK_IN_DOCUMENT_KEY, result = newCollection());
      allHolders.add(holder);
    }
    return result;
  }
private @NotNull <T extends UserDataHolder> ECollection addWeaklyTrackedEmptyStack(@NotNull T holder, @NotNull Collection<? super T> allHolders)