title: Django makemigrations error non-nullable field
body: <blockquote>
    <p>You are trying to add a non-nullable field 'list' to signup without a default; we can't do that (the database needs something to populate existing rows).
    Please select a fix:
     1) Provide a one-off default now (will be set on all existing rows)
     2) Quit, and let me add a default in models.py</p>
  </blockquote>
  
  <p>This is the error for the following code for <code>ArrayField</code>:</p>
  
  <pre><code>from django.contrib.postgres.fields import ArrayField
  from django.db import models
  class signup(models.Model):
      userid=models.CharField(max_length=10)
      password=models.CharField(max_length=10)
      list=ArrayField(models.IntegerField(null=True,blank=True),size=5)
      score=models.IntegerField(default=0)
  </code></pre>