title: Knockout: start observableArray with null
body: <p>Seems that in knockout 3.2.0 they changed the behavior of ObservableArrays. In knockout 2, if I did:</p>
  
  <pre><code>var array = ko.observableArray(null)
  console.log(array())
  </code></pre>
  
  <p>It would return me null. The same thing on knockout 3.2.0 doesn't happen because the observable array instead of null is create as an empty array.</p>
  
  <p>This is my case:</p>
  
  <pre><code>&lt;div&gt;
   &lt;div class="spinner" data-bind="visible: comments() == null"&gt;
   &lt;!-- ko foreach: comments --&gt;
   ...
   &lt;!-- /ko --&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I'd like to start showing in the comments div a spinner, and when the comments are populated, i'll hide the spinner and show the comments. I can't do <code>data-bind="visible: comments().length == 0"</code> because if the post has no comments, the comments array will have 0 length and the spinner will be shown forever.</p>
  
  <p>How can I make this work?</p>