def test_none_as_null(self):
        p1 = Poll(question='Why?')
        p1.save()
        c1 = Choice(poll=p1, choice='Because.')
        c1.save()
        c2 = Choice(poll=p1, choice='Why Not?')
        c2.save()

        # Exact query with value None returns nothing ("is NULL" in sql,
        # but every 'id' field has a value).
        self.assertQuerysetEqual(Choice.objects.filter(choice__exact=None), [])

        # Excluding the previous result returns everything.
        self.assertQuerysetEqual(
                Choice.objects.exclude(choice=None).order_by('id'),
                [
                    '<Choice: Choice: Because. in poll Q: Why? >',
                    '<Choice: Choice: Why Not? in poll Q: Why? >'
                ]
        )

        # Valid query, but fails because foo isn't a keyword
        self.assertRaises(FieldError, Choice.objects.filter, foo__exact=None)

        # Can't use None on anything other than __exact
        self.assertRaises(ValueError, Choice.objects.filter, id__gt=None)

        # Can't use None on anything other than __exact
        self.assertRaises(ValueError, Choice.objects.filter, foo__gt=None)

        # Related managers use __exact=None implicitly if the object hasn't been saved.
        p2 = Poll(question="How?")
        self.assertEqual(repr(p2.choice_set.all()), '[]')
Regression test for the use of None as a query value.
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.3/tests/regressiontests/null_queries/tests.py/NullQueriesTests.test_none_as_null