title: Change FormControl value from object (FormGroup) to null and vise versa in Angular 2
body: <p>I have a Form object built with FormBuilder. One of the part of the form needs to be changed dynamically: </p>
  
  <pre><code>"Tag": 
    {
       "Id": 10,
       "Name": "Program43",
       "Source": "DSN"
    }
  </code></pre>
  
  <p>I need to change value in "Tag" to null to have:</p>
  
  <pre><code> "Tag": null
  </code></pre>
  
  <p>and later in the form to have something like:</p>
  
  <pre><code>"Tag": 
    {
       "Id": null,
       "Name": null,
       "Source": null
    }
  </code></pre>
  
  <p>Any idea of best approach to do it? What method of angular2 is the best to use for this?</p>