code: public static <T extends GraphNode<T>> String printTree(T node, Formatter<T> formatter) {
          checkArgNotNull(formatter, "formatter");
          return printTree(node, formatter, Predicates.<T>alwaysTrue(), Predicates.<T>alwaysTrue());
      }
docs: Creates a string representation of the graph reachable from the given node using the given formatter.
  
  @param node      the root node
  @param formatter the node formatter
  @return a new string