title: Django ArrayField null=True migration with Postgresql
body: <p>So in Django docs for creating new fields on Postgresql it says (<a href="https://docs.djangoproject.com/en/1.9/topics/migrations/#postgresql" rel="noreferrer">Full description</a>):</p>
  
  <blockquote>
    <p>... it’s recommended you always create new columns with <code>null=True</code>, as this way they will be added immediately.</p>
  </blockquote>
  
  <p>What if I want to create an ArrayField, something like this: </p>
  
  <pre><code>tags = ArrayField(models.CharField(max_length=255, blank=True, default=''), default=list, null=True)
  </code></pre>
  
  <p>Should I also pass <code>null=True</code> into <code>CharField</code> which is inside this <code>ArrayField</code>?</p>