title: Why arrays in Immutable.js records are mutable?
body: <p>I noticed that in the following piece of code</p>
  
  <pre><code>const TaskRecord = new Immutable.Record({
    name: '',
    requiredFor: [],
  });
  
  class Task extends TaskRecord {
  }
  
  const task = new Task();
  </code></pre>
  
  <p><code>task.requiredFor</code> is really an array (calling <code>get('requiredFor')</code> inside the Task class yields the same result) and doesn't get converted to Immutable.List... this way the record isn't immutable.</p>
  
  <p><strong>Why it is this way? How to fix this?</strong></p>