Stack-38950251-nested route problem

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  //this.route('/',{path:'/subcategory'});
  this.route('subcategory',{path:'/:sub_id'},function(){
    this.route('items',{ path: "/:item_id"  });
  });
});

export default Router;

routes.subcategory.items.js

import Ember from 'ember';

export default Ember.Route.extend({
  model(params){
    console.log('model in items : '+params.item_id);
    var result = 'result '+params.item_id;
    return [result];
  }
});

routes.subcategory.js

import Ember from 'ember';

export default Ember.Route.extend({
  model(params){
    console.log('subcategory model : params.sub_id '+params.sub_id);
    return [{id:1,title:'title1'},{id:2,title:'title2'}];
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.subcategory.hbs

<div class="todo">
            <ul class="todo-list">
              {{#each model as |category|}}
              <li>

                <span class="desc">{{category.title}} {{category.id}}</span>
   
    {{#link-to 'subcategory.items' category.id }}Hiii
    {{/link-to}} 



              </li>
              {{/each}}

            </ul>
          </div>
{{outlet}}

templates.subcategory.items.hbs

items

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}