code: public static <N> ImmutableGraph<N> singletonGraph(Graph<N> graph, N node) {
          final MutableGraph<N> mutableGraph = GraphBuilder.from(graph).build();
          mutableGraph.addNode(node);
          return ImmutableGraph.copyOf(mutableGraph);
      }
docs: Returns an immutable graph, containing only the specified node.
  
  @param graph The graph to use as template for the created graph
  @param node  The single node in the returned graph
  @param <N>   The class of the nodes
  @return an immutable graph with a single node
  @see GraphBuilder#from(Graph)