Cannot get objects when an attribute is None

[John <john@…>]

I have a model defined like this:

class Reported(models.Model):
    user = models.ForeignKey(User, null=True)
    link = models.ForeignKey(Link)
    date = models.DateTimeField(auto_now_add=True)

but when I execute this on the shell, it gives an erroneous result.

>>> Reported.objects.create(user=None, link=Link.objects.get(id=2))
<Reported: Reported object>
>>> Reported.objects.get(user=None, link=Link.objects.get(id=2))
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:\Python25\lib\site-packages\django\db\models\manager.py", line 69, in
get
    return self.get_query_set().get(*args, **kwargs)
  File "C:\Python25\lib\site-packages\django\db\models\query.py", line 263, in g
et
    raise self.model.DoesNotExist, "%s matching query does not exist." % self.mo
del._meta.object_name
DoesNotExist: Reported matching query does not exist.

As you can see, I first create an object, and then search for it, but the just-created item cannot be found! This only happens when one of the search fields is None, the following works:

Reported.objects.get(link=Link.objects.get(id=2))

[Alex Gaynor]

This query should be performed using isnull: ​http://www.djangoproject.com/documentation/db-api/#isnull