Allow serializing NoneType in migrations

[Daan van der Kallen]

When in a deconstructible class used in a migration one of the arguments to instantiate the class is the NoneType (aka type(None)) this is just serialized as NoneType which will throw a NameError because it is not defined. The only way to get this value in Python 3 is with type(None) so simply serializing NoneType as type(None) should already do the trick.

[Patrik Sletmo]

I've managed to reproduce the issue and will attempt to provide a patch later this week. If anyone is interested in reproducing the issue on their own, the following code generates a problematic migration:

from django.db import models
from django.utils.deconstruct import deconstructible


@deconstructible
class SerializableClass:
    def __init__(self, foo):
        self.foo = foo


class DemoModel(models.Model):
    problematic_field = models.Field(default=SerializableClass(type(None)))

[Tim Graham <timograham@…>]

In adfdb9f1:

Fixed #29814 -- Added support for NoneType serialization in migrations.