title: Cannot read property '$pristine' of undefined when string used as input name
body: <p>In my form I have an ng-repeat and within that ng-repeat I have a bunch of fields. Sometimes there could be 3 fields, sometimes there might just be one. </p>
  
  <p>I have an angular for each to check $pristine for a specific field. The name of the field pretty much stays the same but the field count number changes so I thought I would check it like this:</p>
  
  <pre><code>var price = "price_" + product.line_no;
  
  console.log($scope.myform.price.$pristine); = console.log($scope.myform."price_1".$pristine);
  </code></pre>
  
  <p>But I am getting this:</p>
  
  <pre><code>TypeError: Cannot read property '$pristine' of undefined
  </code></pre>