title: Expected expression in form of '_item_ in _collection_[ track by _id_]' but got ''
body: <p>In my ng-repeats I get error: </p>
  
  <blockquote>
    <p>"Error: [ngRepeat:iexp] Expected expression in form of '<em>item</em> in
    <em>collection</em>[ track by <em>id</em>]' but got ''.</p>
  </blockquote>
  
  <p>Even if this error appears application is not broken and works just fine, however nobody like huge errors in their console. What might cause it? How do I fix it? </p>
  
  <p>I have this ng-repeat code in my view:</p>
  
  <pre><code>  &lt;div class="input-dual" ng-controller="DateCtrl"&gt;
      &lt;div class="input-dual-inner"&gt;
        &lt;span&gt;Datum polaska:&lt;/span&gt;
        &lt;select&gt;
          &lt;option&gt;-&lt;/option&gt;
          &lt;option ng-repeat="year in years"&gt;{{year}}&lt;/option&gt;
        &lt;/select&gt;
      &lt;/div&gt;
      &lt;div class="input-dual-inner"&gt;
        &lt;select&gt;
          &lt;option&gt;-&lt;/option&gt;
          &lt;option ng-repeat="month in months"&gt;{{month.name}}&lt;/option&gt;
        &lt;/select&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  </code></pre>
  
  <p>and this is the controller for it:</p>
  
  <pre><code>AppControllers.controller('DateCtrl', [
    '$scope','$http',
    function($scope, $http){
      $http.get('/dates').then(function(response){
        $scope.years = response.data.years
        $scope.months = []
        for (var i = 0; i &lt; 12; i++) {
          $scope.months.push(response.data.months[i])
        }
      })
    }
  ]);
  </code></pre>
  
  <p>This is how JSON file looks like:</p>
  
  <pre><code>{"years":[2016,2017],"months":[{"no":"01","name":"Siječanj"},{"no":"02","name":"Veljača"},{"no":"03","name":"Ožujak"},{"no":"04","name":"Travanj"},{"no":"05","name":"Svibanj"},{"no":"06","name":"Lipanj"},{"no":"07","name":"Srpanj"},{"no":"08","name":"Kolovoz"},{"no":"09","name":"Rujan"},{"no":"10","name":"Listopad"},{"no":"11","name":"Studeni"},{"no":"12","name":"Prosinac"}]}
  </code></pre>