title: Django makemigrations works, migrate fails with "django.db.utils.IntegrityError: NOT NULL constraint failed"
body: <p>I'm stuck. Django 1.7, SQLite3.</p>
  
  <p>I've changed my model to add the <code>thumbnail</code> column, as in <a href="https://www.youtube.com/watch?v=b43JIn-OGZU" rel="noreferrer">this tutorial</a>. It was this:</p>
  
  <pre><code>from django.db import models
  
  class Article(models.Model):
      title = models.CharField(max_length=200)
      body = models.TextField()
      pub_date = models.DateTimeField('date published')
      likes = models.IntegerField(default=0)
  
      def __str__(self):
          return  self.title
  </code></pre>
  
  <p>and is now this:</p>
  
  <pre><code>from django.db import models
  from time import time         
  
  def get_upload_file_name(instance, filename):
      return  "uploaded_files/%s_%s" % (str(time()).replace(".", "_"), filename)
  
  class Article(models.Model):
      title = models.CharField(max_length=200)
      body = models.TextField()
      pub_date = models.DateTimeField('date published')
      likes = models.IntegerField(default=0) 
      thumbnail = models.FileField(upload_to=get_upload_file_name, null=True)
  
      def __str__(self):
          return  self.title
  </code></pre>
  
  <p>I backed up all data to a json text file with </p>
  
  <pre><code>python manage.py dumpdata article --indent=4 &gt; article.json
  </code></pre>
  
  <p>and then executed</p>
  
  <pre><code>python manage.py makemigrations
  </code></pre>
  
  <p>which worked. But </p>
  
  <pre><code>python manage.py migrate
  </code></pre>
  
  <p>fails with</p>
  
  <p><code>django.db.utils.IntegrityError: NOT NULL constraint failed: article_article__new.thumbnail</code></p>
  
  <p>And now, even after adding <code>null=True</code> to the <code>thumbnail</code> line in <code>models.py</code>, running <code>makemigrations</code> succeeds, and <code>migrate</code> fails the same way.</p>
  
  <p>What do I do?</p>