title: django - TypeError: expected string or buffer
body: <p>Hello I added a field to a model and when I try to do <code>migrate</code> in terminal it give me this error, does anyone know what this might be?</p>
  
  <p>=========================================================================</p>
  
  <pre><code>  File "manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
      utility.execute()
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
      self.fetch_command(subcommand).run_from_argv(self.argv)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
      self.execute(*args, **options.__dict__)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute
      output = self.handle(*args, **options)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 161, in handle
      executor.migrate(targets, plan, fake=options.get("fake", False))
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/migrations/executor.py", line 68, in migrate
      self.apply_migration(migration, fake=fake)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/migrations/executor.py", line 102, in apply_migration
      migration.apply(project_state, schema_editor)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/migrations/migration.py", line 108, in apply
      operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/migrations/operations/fields.py", line 139, in database_forwards
      schema_editor.alter_field(from_model, from_field, to_field)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/backends/schema.py", line 454, in alter_field
      self._alter_field(model, old_field, new_field, old_type, new_type, old_db_params, new_db_params, strict)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 199, in _alter_field
      self._remake_table(model, alter_fields=[(old_field, new_field)])
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 137, in _remake_table
      self.create_model(temp_model)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/backends/schema.py", line 212, in create_model
      definition, extra_params = self.column_sql(model, field)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/backends/schema.py", line 124, in column_sql
      default_value = self.effective_default(field)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/backends/schema.py", line 187, in effective_default
      default = field.get_db_prep_save(default, self.connection)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 627, in get_db_prep_save
      prepared=False)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 1290, in get_db_prep_value
      value = self.get_prep_value(value)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 1269, in get_prep_value
      value = super(DateTimeField, self).get_prep_value(value)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 1171, in get_prep_value
      return self.to_python(value)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 1228, in to_python
      parsed = parse_datetime(value)
    File "/Users/Derek/.virtualenvs/tasks/lib/python2.7/site-packages/django/utils/dateparse.py", line 70, in parse_datetime
      match = datetime_re.match(value)
  TypeError: expected string or buffer
  </code></pre>
  
  <p>model.py</p>
  
  <pre><code>class Lead(models.Model):
      title = models.CharField(choices=TITLE_CHOICES, max_length=20, blank=True, default='')
      first_name = models.CharField(max_length=80, blank=True, default='')
      last_name = models.CharField(max_length=80, blank=True)
      company = models.CharField(max_length=80, blank=True)
      position = models.CharField(max_length=50, blank=True, default='')
      location = models.CharField(max_length=100, blank=True)
      currently_using_sms = models.CharField(choices=CURRENTLY_USING_SMS, default='',  max_length=30)
      services_interested_in = models.ManyToManyField(Services)
      phone_number = models.CharField(blank=True, max_length=20, default='')
      mobile_number = models.CharField(blank=True, max_length=11, default='')
      email = models.EmailField(blank='True', default='')
      best_day_to_contact = models.DateTimeField(blank=False, null=True)
      notes = models.TextField(blank=True)
      assign_to = models.ForeignKey(User, db_index=True, blank=True, null=True, default=None)
      lead_source = models.ForeignKey(LeadSource, db_index=True, blank=True, null=True)
      status = models.CharField(choices=LEAD_STATUS, max_length=100, default='1')
  </code></pre>