docs: public static synchronized RenderEngine getInstance() {
      //availableEngines = null;
      if (null == availableEngines) {
        availableEngines = new HashMap();
      }
  
      if (!availableEngines.containsKey(DEFAULT)) {
        RenderEngine engine = new BaseRenderEngine();
        availableEngines.put(engine.getName(), engine);
      }
  
      return (RenderEngine) availableEngines.get(DEFAULT);
    }