不好意思，我是新手，我按文档试了一下DB+RECORD 总出错，也不知错在那里，各位可否帮看一下？

Exception in thread "main" java.lang.NullPointerException

at com.jfinal.plugin.activerecord.Db.save(Db.java:390)

at demo.genclass.main(genclass.java:25)

C:\Users\lijing\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java returned: 1

我的测试代码：

   public static void main(String[] args) {

  Record user = new Record().set("username", "James") ;

  Db.save("User", user);

    }

///配置类

public class DemoConfig extends JFinalConfig {

    @Override

    public void configConstant(Constants me) {

        me.setViewType(ViewType.JSP);

        me.setDevMode(true);

    }

    @Override

    public void configRoute(Routes me) {

        me.add("/hello", HelloController.class);

    }

    @Override

    public void configPlugin(Plugins me) {

           C3p0Plugin cp = new C3p0Plugin("jdbc:mysql://127.0.0.1:3306/blog", "root", "lzlife");

        me.add(cp);

        ActiveRecordPlugin arp = new ActiveRecordPlugin(cp);

      arp.setShowSql(true) ;

        me.add(arp);

        arp.addMapping("user", User.class);

    }

    @Override

    public void configInterceptor(Interceptors me) {

    }

?

    @Override

    public void configHandler(Handlers me) {

    }

}