What's the meaning of "?" in {{hero?.name}} : <p>what does means "?" in the following code:</p>

<pre><code>  &lt;span [style.text-decoration]="lineThrough"&gt;
     {{prefix}} {{hero?.name}}
  &lt;/span&gt;
</code></pre>

<p>I don't understand the "?" in {{hero?.name}}.
This code is in documentation of Angular:
   <a href="https://angular.io/guide/template-syntax#custom-events-with-eventemitter" rel="nofollow noreferrer">https://angular.io/guide/template-syntax#custom-events-with-eventemitter</a></p>

<p>Thanks</p>
