code: @SafeVarargs
      public static <N, E> void write(Graph<N, E> graph,
                                      Appendable a,
                                      VisualizationHelper<N, ? super E>... additionalHelpers) throws IOException {
          write(graph, a, Arrays.asList(additionalHelpers));
      }
docs: Renders a {@link Graph} in the GraphVIZ DOT format.
  
  @param graph
  the graph to render
  @param a
  the appendable to write to.
  @param additionalHelpers
  additional helpers for providing visualization properties.
  
  @throws IOException
  if writing to {@code a} fails.