title: VueJs v-for how to check list undefined before continue
body: <p>Refer to the template below, how to add condition to make sure the <code>menu</code> is not <code>undefined</code> inside the <code>v-for</code> attribute? </p>
  
  <p>I've tried <code>v-for="menu?item in menu.items:[]"</code> and <code>v-for="item in menu?.items"</code> but neither works.</p>
  
  <pre><code>&lt;div v-for="item in menu.items"&gt;{{item.text}}&lt;/div&gt;
  </code></pre>