title: Multiple classes in ngClass
body: <p>I'm trying to add multiple values in *ngClass, what used to work on previous alpha releases and doesn't seem to work now on angular2 beta:</p>
  
  <pre><code>&lt;i *ngClass="['fa','fa-star']"&gt;&lt;/i&gt;
  </code></pre>
  
  <p>It produces an error:</p>
  
  <blockquote>
    <p>EXCEPTION: TypeError: Cannot read property 'add' of undefined in
    [['fa','fa-star'] in PostView@30:27]</p>
  </blockquote>
  
  <p>What am I missing here?</p>