code: public RendererBuilder<T> withPrototype(Renderer<? extends T> renderer) {
      if (renderer == null) {
        throw new NeedsPrototypesException(
            "RendererBuilder can't use a null Renderer<T> instance as prototype");
      }
      this.prototypes.add(renderer);
      return this;
    }
docs: Add a Renderer instance as prototype.
  
  @param renderer to use as prototype.
  @return the current RendererBuilder instance.