title: Django - null value in column "wins" violates not-null constraint
body: <p>When i'm trying to create a user in django with admin or by my register function in views, it gives me this error:</p>
  
  <p>by register function:</p>
  
  <pre><code>IntegrityError at /register_user/
  null value in column "wins" violates not-null constraint
  DETAIL:  Failing row contains (3, pbkdf2_sha256$36000$3SoR8l6dEXRD$CkFB+RRKeJPUPeux4EByqkYFkGLgkhI..., null, f, Ion, , , ion@pidginhost.com, f, t, 2017-05-08 10:47:39.860612+00, f, null).
  </code></pre>
  
  <p>by add user in admin</p>
  
  <pre><code>IntegrityError at /admin/football_app/customuser/add/
  null value in column "wins" violates not-null constraint
  DETAIL:  Failing row contains (7, pbkdf2_sha256$36000$o6UGPqAw72hi$qfbgoRAoJn4WmlK010VbfCzeu3+Fo0w..., null, f, Ion, , , , f, t, 2017-05-08 11:02:54.725688+00, f, null).
  </code></pre>
  
  <p>models.py</p>
  
  <pre><code>class CustomUser(AbstractUser):
      selected = models.BooleanField(default=False)
      wins = models.IntegerField()
      REQUIRED_FIELDS = ['email', 'selected', 'wins']
  
      def __str__(self):
          return self.username
  
  
  class Score(models.Model):
      VALUE = (
          (1, "Score 1"),
          (2, "Score 2"),
          (3, "Score 3"),
          (4, "Score 4"),
          (5, "Score 5"),
          (6, "Score 6"),
          (7, "Score 7"),
          (8, "Score 8"),
          (9, "Score 9"),
          (10, "Score 10"),
      )
      granted_by = models.ForeignKey(settings.AUTH_USER_MODEL, default=0)
      granted_to = models.ForeignKey(settings.AUTH_USER_MODEL, default=0, related_name='granted_to')
      grade = models.PositiveSmallIntegerField(default=0, choices=VALUE)
  
      def __str__(self):
          return str(self.granted_to)
  </code></pre>
  
  <p>views.py</p>
  
  <pre><code>def register_user(request):
      data = dict()
      if request.method == 'POST':
          form = UserForm(request.POST)
          if form.is_valid():
              user = form.save(commit=False)
              user.set_password(user.password)
              user.save()
              return redirect('/login/')
      else:
          data['form'] = UserForm()
      return render(request, 'register_user.html', data)
  </code></pre>
  
  <p>I'm using the wins field to add +1 to Users and i'm doing it with this in other function in views:</p>
  
  <pre><code>User.objects.filter(username__in=data['d1']).update(wins=F('wins') + 1)
  </code></pre>