code: private <IPW extends IndentingPrintWriter> IPW writeNameTo(IPW output) {
          output.append(name.isEmpty() ? "unnamed" : name).whitespace();
          return output;
      }
docs: Adds the package name to the diagram.
  Re: bug 107: If the package name is empty (i.e. the 'default' package),
  render {@code "unnamed"} because an empty name is not valid in PlantUML.
  
  @param output The output to append the package name to.
  @param <IPW>  The type of the output object.
  @return The same output instance for method chaining.