private VirtualFilePointerContainer createContainer(@NotNull Collection<String> urls) {
    // optimization: avoid creating heavy container for empty list, use 'EMPTY' stub for that case
    VirtualFilePointerContainer container;
    if (urls.isEmpty()) {
      container = EMPTY;
    }
    else {
      container = VirtualFilePointerManager.getInstance().createContainer(myRootsDisposable);
      ((VirtualFilePointerContainerImpl)container).addAll(urls);
    }
    return container;
  }
private VirtualFilePointerContainer createContainer(@NotNull Collection<String> urls)