CharSequence toCharSequence() {
      if (arity == 0) {
        CharConsumer consumer = new CharConsumer();
        invoke(new Invokation(consumer));
        CharSequence cs = consumer.asCharSequence();
        return cs;
      }
      return super.toString();
    }
@param arity number of fragment parameters
generator/src/org/immutables/generator/Templates.java