Annotation with `Case` can't be used with `exclude`

[Ram Rachum]

When you define an annotation that uses Case, you can use .filter on it but you can't use .exclude. (You get various exceptions about .null and .get_col not existing.)

Example:

def my_view(request, *args, **kwargs):
    things = models.Thing.objects.all().annotate(
        bar=django.db.models.Case(
            django.db.models.When(
                foo='foo',
                then=django.db.models.Value('bar')
            ),
            default=django.db.models.Value('baz'),
            output_field=django.db.models.CharField()
        )
    )
    
    print(things.filter(bar='bar')) # This one works
    print(things.exclude(bar='bar')) # This one doesn't 
    return django.http.HttpResponse(str(things))

Full working example attached to this ticket. (Simply run migrate, then runserver, then access the root URL to see the Django debug page for the exception.)

[Ram Rachum]

Full working example, run migrate then runserver then access root url to see the exception