title: Altered Django model. I provided a one-off default = datetime.date for DateField. Found that it's invalid. Removed the field and still can't migrate
body: <p>Hi here's the specific line that I added in models.py</p>
  
  <p><code>billingMonth2 = models.DateTimeField()</code></p>
  
  <p>This is what happened in makemigrations, I figured I added a non nullable field so I tried to define a default value:</p>
  
  <pre><code>    You are trying to add a non-nullable field 'billingMonth' to bills 
      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
      Select an option: 1
      Please enter the default value now, as valid Python
      The datetime and django.utils.timezone modules are available, so you can do 
      e.g. timezone.now()
      &gt;&gt;&gt; datetime.date
      Migrations for 'bills':
      0007_auto_20160609_1400.py:
      - Change Meta options on bills
      - Add field billingMonth to bills
  </code></pre>
  
  <p>I found out that datetime.date was invalid and came out with an error</p>
  
  <pre><code>    ....File "/home/jrbenriquez/Envs/env1/local/lib/python2.7/site-packages/django/db/backends/base/schema.py", line 197, in effective_default
  default = field.get_default()
      File "/home/jrbenriquez/Envs/env1/local/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 797, in get_default
  return self.default()
      TypeError: Required argument 'year' (pos 1) not found
  </code></pre>
  
  <p>So I just removed the billingMonth2 field hoping it would go back to normal and also setting a default value  as</p>
  
  <pre><code>    `billingMonth2 = models.DateTimeField(default='Test',null=True,blank=True)`
  </code></pre>
  
  <p>Both still gives the same error. 
  It seems to me I have changed something within the meta of the model in some other file or in the database and that I have to delete the default value "datetime.date" somewhere</p>
  
  <p>I hope someone could help me here. Thanks!</p>
  
  <p>UPDATE:
  Here's 0007_auto20160609_1400.py</p>
  
  <pre><code>    # -*- coding: utf-8 -*-
      # Generated by Django 1.9.6 on 2016-06-09 14:00
      from __future__ import unicode_literals
  
      from django.db import migrations, models
      import django.utils.datetime_safe
  
  
      class Migration(migrations.Migration): 
  
          dependencies = [
              ('bills', '0006_bills_duedate'),
          ]
  
          operations = [
              migrations.AlterModelOptions(
                  name='bills',
                  options={'ordering': ('-id', '-status'),     'verbose_name_plural': 'Bills'},
               ),
              migrations.AddField(
                  model_name='bills',
                  name='billingMonth',
                  field=models.DateField(default=django.utils.datetime_safe.date),
                  preserve_default=False,
               ),
  ]
  </code></pre>