title: AngularJS - Form Custom Validation - Check if at least one input is empty
body: <p>Given a simple html form like this:</p>
  
  <pre><code>&lt;form name="myForm" action="#sent" method="post" ng-app&gt;
     &lt;input name="userPreference1" type="text" ng-model="shipment.userPreference" /&gt;
     &lt;input name="userPreference1" type="text" ng-model="shipment.userPreference" /&gt;
     &lt;input name="userPreference1" type="text" ng-model="shipment.userPreference" /&gt;
  ... submit input and all the other code...
  &lt;/form&gt;
  </code></pre>
  
  <p>I need your help to know how to check on validation time, if at least one of the inputs is empty. The desired validation is the following. The user must complete at least one a preference.</p>
  
  <p>Using jQuery this:</p>
  
  <pre><code>if ( $("input").val() == "" ) {
  </code></pre>
  
  <p>Works ok, but would like to figure out how to do the same thing using angular.</p>
  
  <p>Thanks so much in advance,</p>
  
  <p>Guillermo</p>