Bug in admin models?

I am trying to add a model entry, via the admin; I get this error (which has not happened before), running Django on Ubuntu 12.04 with the test server.  Not sure if there is an error with the model (which has worked fine up to now) or ...?


Request Method: POST
Request URL: http://127.0.0.1:8000/admin/myapp/mymodel/add/

Django Version: 1.5.4
Python Version: 2.7.3
Installed Applications:
('django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.staticfiles',
 'django.contrib.messages',
 'django.contrib.admindocs',
 'django_nose',
 'django_extensions',
 'crispy_forms',
 'autocomplete_light',
 'admin_enhancer',
 'smart_selects',
 'selectable',
 'massadmin',
 's2.myapp,
 'suit',
 'django.contrib.admin')
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',
 's2s.middle.middleware.AdminSessionMiddleware')


Traceback:
File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  115.                         response = callback(request, *callback_args, **callback_kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in wrapper
  372.                 return self.admin_site.admin_view(view)(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
  91.                     response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/views/decorators/cache.py" in _wrapped_view_func
  89.         response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/sites.py" in inner
  202.             return view(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapper
  25.             return bound_func(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
  91.                     response = view_func(request, *args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in bound_func
  21.                 return func(self, *args2, **kwargs2)
File "/usr/local/lib/python2.7/dist-packages/django/db/transaction.py" in inner
  223.                 return func(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in add_view
  1009.                 self.log_addition(request, new_object)
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/options.py" in log_addition
  530.             action_flag     = ADDITION
File "/usr/local/lib/python2.7/dist-packages/django/contrib/admin/models.py" in log_action
  18.         e = self.model(None, None, user_id, content_type_id, smart_text(object_id), object_repr[:200], action_flag, change_message)

Exception Type: TypeError at /admin/myapp/mymodel/add/
Exception Value: 'NoneType' object has no attribute '__getitem__'

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