title: Immutable.Js - Add new property in Map
body: <p>So let's say that I make a REST API call and receive a JSON in this format:</p>
  
  <pre><code>{
      "plan": {
          "createdDate": "05/04/2017",
          "location": {
            "city": null
            "state": null
          }
          "family": null
      }
  }
  </code></pre>
  
  <p>And within in my reducer, make the JSON as an immutable as so:</p>
  
  <pre><code>Immutable.Map(Immutable.fromJS(action.json))
  </code></pre>
  
  <p>Along the way, is it possible to add properties under <code>family</code>?</p>
  
  <p>For instance, when I am submitting a form to a server, ideally I like to send something like this:</p>
  
  <pre><code>{
      "plan": {
          "createdDate": "05/04/2017",
          "location": {
            "city": null
            "state": null
          }
          "family": {
            "father": "Homer",
            "mother": "Marge",
            "son": "Bartholomew"
          }
      }
  }
  </code></pre>
  
  <p>Or do I have to initialized first to have those properties under <code>family</code> from the start?</p>