TypeError at /admin/models/page/add/
%d format: a number is required, not NoneType

Environment:

Request Method: POST
Request URL: http://***.com/admin/models/page/add/
Django Version: 1.2.4
Python Version: 2.6.4
Installed Applications:
['django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.sites',
'django.contrib.messages',
'django.contrib.admin',
'django.contrib.admindocs',
'plast.models']
Installed Middleware:
('django.middleware.common.CommonMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware')


Traceback:
File "/usr/local/python26/lib/python2.6/site-packages/django/core/handlers/base.py" in get_response
  100.                     response = callback(request, *callback_args, **callback_kwargs)
File "/usr/local/python26/lib/python2.6/site-packages/django/contrib/admin/options.py" in wrapper
  265.                 return self.admin_site.admin_view(view)(*args, **kwargs)
File "/usr/local/python26/lib/python2.6/site-packages/django/utils/decorators.py" in _wrapped_view
  76.                     response = view_func(request, *args, **kwargs)
File "/usr/local/python26/lib/python2.6/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
  78.         response = view_func(request, *args, **kwargs)
File "/usr/local/python26/lib/python2.6/site-packages/django/contrib/admin/sites.py" in inner
  190.             return view(request, *args, **kwargs)
File "/usr/local/python26/lib/python2.6/site-packages/django/utils/decorators.py" in _wrapper
  21.             return decorator(bound_func)(*args, **kwargs)
File "/usr/local/python26/lib/python2.6/site-packages/django/utils/decorators.py" in _wrapped_view
  76.                     response = view_func(request, *args, **kwargs)
File "/usr/local/python26/lib/python2.6/site-packages/django/utils/decorators.py" in bound_func
  17.                 return func(self, *args2, **kwargs2)
File "/usr/local/python26/lib/python2.6/site-packages/django/db/transaction.py" in _commit_on_success
  299.                     res = func(*args, **kw)
File "/usr/local/python26/lib/python2.6/site-packages/django/contrib/admin/options.py" in add_view
  803.             if form.is_valid():
File "/usr/local/python26/lib/python2.6/site-packages/django/forms/forms.py" in is_valid
  121.         return self.is_bound and not bool(self.errors)
File "/usr/local/python26/lib/python2.6/site-packages/django/forms/forms.py" in _get_errors
  112.             self.full_clean()
File "/usr/local/python26/lib/python2.6/site-packages/django/forms/forms.py" in full_clean
  269.         self._post_clean()
File "/usr/local/python26/lib/python2.6/site-packages/django/forms/models.py" in _post_clean
  337.             self.instance.clean_fields(exclude=exclude)
File "/usr/local/python26/lib/python2.6/site-packages/django/db/models/base.py" in clean_fields
  926.                 setattr(self, f.attname, f.clean(raw_value, self))
File "/usr/local/python26/lib/python2.6/site-packages/django/db/models/fields/__init__.py" in clean
  195.         self.run_validators(value)
File "/usr/local/python26/lib/python2.6/site-packages/django/db/models/fields/__init__.py" in run_validators
  150.                 v(value)
File "/usr/local/python26/lib/python2.6/site-packages/django/core/validators.py" in __call__
  146.                 self.message % params,
File "/usr/local/python26/lib/python2.6/site-packages/django/utils/functional.py" in __mod__
  227.                 return unicode(self) % rhs

Exception Type: TypeError at /admin/models/page/add/
Exception Value: %d format: a number is required, not NoneType

class Page(models.Model):
    title_ru = models.CharField(max_length = 255, verbose_name='Title (ru)')
    title_ua = models.CharField(max_length = 255, verbose_name='Title (ua)')
    header_ru = models.CharField(max_length = 100, verbose_name='Заголовок (ru)')
    header_ua = models.CharField(max_length = 100, verbose_name='Заголовок (ua)')
    text_ru = models.TextField(verbose_name = 'Текст (ru)')
    text_ua = models.TextField(verbose_name = 'Текст (ua)')
    description_ru = models.CharField(blank=True, null=True, verbose_name='Meta описание (ru)')
    description_ua = models.CharField(blank=True, null=True, verbose_name='Meta описание (ua)')
    keywords_ru = models.CharField(blank = True, null = True, verbose_name='Meta ключевые слова (ru)')
    keywords_ua = models.CharField(blank = True, null = True, verbose_name='Meta ключевые слова (ua)')
    url = models.CharField(blank=True, null=True, max_length = 30, verbose_name='URL (например about)')
    
    class Meta:
        ordering = ['header_ru']
    
    def __unicode__(self):
        return self.header_ru
    
    @permalink
    def get_absolute_url(self):
        return('page_detail', None, {'object_id': self.url})

    @permalink
    def get_absolute_url(self):
        return('page_detail', None, {'object_id': self.url})