title: Null in API version Android Studio preview
body: <p>I updated from Android Studio 2.3 to 3.0 and now none of the previews on the XML editors are shown.</p>
  
  <p>I can see a null in the top bar in the API level selector and it does not give me any option to pick</p>
  
  <p><a href="https://i.stack.imgur.com/2nAax.png" rel="noreferrer"><img src="https://i.stack.imgur.com/2nAax.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/fXNyR.png" rel="noreferrer"><img src="https://i.stack.imgur.com/fXNyR.png" alt="enter image description here"></a></p>
  
  <p>Any possible solution for that?</p>
  
  <p>I tried Invalidate cache and restart but it does not seem to help.</p>