public static @NotNull <K, V> MultiMap<DataNode<K>, DataNode<V>> groupBy(@NotNull Collection<? extends DataNode<V>> nodes, final @NotNull Key<K> key) {
    return ContainerUtil.groupBy(nodes, node -> node.getDataNode(key));
  }
public static @NotNull <K, V> MultiMap<DataNode<K>, DataNode<V>> groupBy(@NotNull Collection<? extends DataNode<V>> nodes, final @NotNull Key<K> key)