[sonata admin] argument "$code" of method

2. CREATING AN ADMIN

按照这里，在 AppBundle中的Controller创建了 CategoryAdmin 类，当运行

php bin/console server:start

出现

Cannot autowire service "AppBundleControllerCategoryAdmin": argument "$code" of method "SonataAdminBundleAdminAbstractAdmin::__construct()" has no  
   type-hint, you should configure its value explicitly. 

通过搜索资料，找到 Empty Dashboard Symfony3 sonata adminBundle 最后比对才发现，需要把 src/AppBundle/Controller/CategoryAdmin.php 放入到 src/AppBundle/Admin/CategoryAdmin.php ，
然后再运行 php bin/console server:start 就启动成功了

最终的效果