title: Angular Material : make a md-radio-group required
body: <p>I am working with Angular Material, I need to make a radio group required, so that the user has to select a radio button, before he can submit the form.
  So the form should be invalid while no radio button is selected.</p>
  
  <p>this is the code</p>
  
  <pre><code>&lt;form id="pipelineForm" name="pipelineForm" ng-submit="processForm()" flex layout="column" novalidate&gt;
      &lt;md-radio-group ng-model="parameters.selected" ng-required="true" name="analyzerRG" 
                &lt;md-radio-button ng-value="choiceObj" ng-repeat="choiceObj in parameters.choices" ng-required&gt;
                {{choiceObj.text}}
                &lt;/md-radio-button&gt;
      &lt;/md-radio-group&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>i have tried making individual <code>&lt;md-radio-button&gt;</code> required, giving <code>name</code> to the radio group and using <code>ng-messages</code> for <code>required</code> , but to no avail.
  When i check the <code>md-radio-group</code> in chrome element inspector, it always has the <code>class="ng-valid ng-valid-required"</code> .</p>
  
  <p>I can probably check the <code>parameters.selected</code> property for validating the form on my own, but i would like if the correct classes are applied to the <code>md-radio-group</code> and so the form is automatically invalid.</p>
  
  <p>P.S. : There is a similar issue on Angular Material Github, but it seems to be closed now and the suggestions do not seem to work for me.</p>