title: ng-repeat filter "show all" items if no filter selected
body: <p>I have an <code>ng-repeat</code> filter that uses a <code>&lt;select&gt;</code> menu to filter through a bunch of countries.</p>
  
  <p>For example:</p>
  
  <pre><code>&lt;div class="col-md-3 col-sm-6" ng-repeat="item in listings | filter: { location: locationFilter }"&gt;
  </code></pre>
  
  <p>How can I make it so that if nothing is selected, it automatically shows ALL the countries? And only starts filtering once a particular country is selected?</p>
  
  <p>I'm sure this is probably a simple question but I am quite new to this and couldn't find how to do it.</p>
  
  <p>Thanks!</p>