title: angular input checkbox remove field
body: <p>I'm fighting with angular input checkboxes.  I have a simple input that looks like this...</p>
  
  <pre><code>&lt;input type="checkbox" ng-model="selectedExercise.isTimed"   required/&gt;
  </code></pre>
  
  <p>However, when I uncheck the box it removes the .isTimed field from my object, when I want to set it equal to false.  For example...</p>
  
  <p>checked</p>
  
  <pre><code>{
    "name": "Work",
    "isTimed": true,
    "duration": 3,
  }
  </code></pre>
  
  <p>unchecked</p>
  
  <pre><code>{
    "name": "Work",
    "duration": 3,
  }
  </code></pre>
  
  <p>I have hacked this to work by adding an ng-change function, but it is super hack in that it just checks to see if angular removed the field, then re-adds it.  Is there a proper way to setup my input checkbox so angular won't remove the object field when the box is unchecked?</p>