AttributeError: 'NoneType' object has no attribute 'find' when hiding announcement

```
Traceback (most recent call last):
  File "/home/vagrant/env/lib/python2.6/site-packages/django/contrib/staticfiles/handlers.py", line 67, in __call__
    return self.application(environ, start_response)
  File "/home/vagrant/env/lib/python2.6/site-packages/django/core/handlers/wsgi.py", line 241, in __call__
    response = self.get_response(request)
  File "/home/vagrant/env/lib/python2.6/site-packages/django/core/handlers/base.py", line 177, in get_response
    response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
  File "/home/vagrant/env/lib/python2.6/site-packages/django/core/handlers/base.py", line 219, in handle_uncaught_exception
    return debug.technical_500_response(request, *exc_info)
  File "/home/vagrant/env/lib/python2.6/site-packages/django/core/handlers/base.py", line 115, in get_response
    response = middleware_method(request, e)
  File "/home/vagrant/env/lib/python2.6/site-packages/django/core/handlers/base.py", line 109, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/home/vagrant/env/src/django-announcements/announcements/views.py", line 36, in announcement_hide
    return HttpResponseRedirect(redirect_to)
  File "/home/vagrant/env/lib/python2.6/site-packages/django/http/__init__.py", line 747, in __init__
    parsed = urlparse(redirect_to)
  File "/usr/lib/python2.6/urlparse.py", line 108, in urlparse
    tuple = urlsplit(url, scheme, allow_fragments)
  File "/usr/lib/python2.6/urlparse.py", line 147, in urlsplit
    i = url.find(':')
AttributeError: 'NoneType' object has no attribute 'find'
```