GenericForeignKey fails if assigned to an object which implements the __len__ method

[Martin Natano]

Supposing you have a model with a GenericForeignKey:

class Example(models.Model):
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    instance = generic.GenericForeignKey()

and a model which implements the __len__ method:

class Table(models.Model)
    data = models.TextField()

    def __len__(self):
        return 0

If you do

t = Table.object.create()
e = Example()
e.instance = t

you get an error:

Impossible arguments to GFK.get_content_type!

I think this is cause by checking for a logical True value instead of a "not None" comparison.

[Martin Natano]

fix + regressiontest

[Martin Natano]

Replying to Alex:
regression test attached

[Martin Natano]

sry, accidentaly removed the needs_tests flag

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Ramiro Morales]

Duplicate of #13085.