@NotNull
  public Collection<PackagingNodeSource> getNodeSource(@NotNull PackagingElement<?> element) {
    final Collection<PackagingNodeSource> nodeSources = myNodeSources.get(element);
    return nodeSources != null ? nodeSources : Collections.emptyList();
  }
@NotNull
  public Collection<PackagingNodeSource> getNodeSource(@NotNull PackagingElement<?> element)