docs: public static  RuntimeException throwCastException(ClassCastException ex,GroupTemplate gt){
  		String clsName = gt.getConf().getEngine();
  		if(clsName.equals("org.beetl.core.engine.DefaultTemplateEngine")){
  			return ex;
  		}else{
  			String detail = ex.getMessage();
  			detail = detail + "如果采用优化引擎，会假定传给模板的变量是同一类型,如果不是，请使用directive dynamic 变量；来避免";
  			throw new RuntimeException(detail,ex);
  		}
  	}