code: public static <N> ImmutableGraph<N> emptyGraph(Graph<N> graph) {
          return ImmutableGraph.copyOf(GraphBuilder.from(graph).build());
      }
docs: Returns an empty graph (immutable) initialized with all properties queryable from {@code graph}.
  
  @param graph The graph to use as template for the created graph
  @param <N>   The class of the nodes
  @return an empty graph
  @see GraphBuilder#from(Graph)