Ember Cannot read property 'extend' of undefined

the error is Cannot read property 'extend' of undefined,my ember is the newest,and i need some help,please.

App = Ember.Application.create({
    LOG_TRANSITIONS: true
});

App.ApplicationView = Ember.View.extend({
   templateName : 'application1'
});

App.Router.map(function(){
    this.resource("home",{path:"/"});
    this.resource("employee",{path:"/employee/:employee_id"});
});

App.HomeRoute = Ember.Route.extend({
   model : function(){
    return App.Employee.find();
    },
   setupController:function(controller,model){
      controller.set('content',model);  
   }
});