集成arouter，跨module报错

 com.alibaba.android.arouter.exception.HandlerException: ARouter::Extract the default group failed, the path must be start with '/' and contain more than 2 '/'!
        at com.alibaba.android.arouter.launcher._ARouter.extractGroup(_ARouter.java:226)
        at com.alibaba.android.arouter.launcher._ARouter.build(_ARouter.java:187)
        at com.alibaba.android.arouter.launcher.ARouter.build(ARouter.java:141)
        at com.play.module_main.activity.MainActivity$1.onNavigationItemSelected(MainActivity.java:35)
        at android.support.design.widget.BottomNavigationView$1.onMenuItemSelected(BottomNavigationView.java:182)
        at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:822)
        at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:171)
        at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:973)
        at android.support.design.internal.BottomNavigationMenuView$1.onClick(BottomNavigationMenuView.java:95)
        at android.view.View.performClick(View.java:7251)
        at android.view.View.performClickInternal(View.java:7228)
        at android.view.View.access$3500(View.java:802)
        at android.view.View$PerformClick.run(View.java:27843)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7116)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:925)

根据github的使用文档，路由路径至少需要有两级：/xx/xx

public static class Main {
        private static final String MAIN = "/main";
        /*主业务界面*/
        public static final String PAGER_MAIN = MAIN +"/main";
    }