Migration 0035_preference_model_unique still broken

Exception:

Running migrations:
  Applying core.0035_preference_model_unique...Traceback (most recent call last):
  File "/srv/aleksis/envs/production/bin/aleksis-admin", line 8, in <module>
    sys.exit(aleksis_cmd())
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/aleksis/core/__main__.py", line 14, in aleksis_cmd
    execute_from_command_line(sys.argv)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
    utility.execute()
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/core/management/__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/core/management/base.py", line 89, in wrapped
    res = handle_func(*args, **kwargs)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/core/management/commands/migrate.py", line 244, in handle
    post_migrate_state = executor.migrate(
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/db/migrations/executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/db/migrations/executor.py", line 227, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/db/migrations/migration.py", line 126, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/django/db/migrations/operations/special.py", line 190, in database_forwards
    self.code(from_state.apps, schema_editor)
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/aleksis/core/migrations/0035_preference_model_unique.py", line 35, in _migrate_preference_models_to_unique
    if BasePreferenceModel.get_value(obj) == BasePreferenceModel.preference(obj).default or found:
  File "/srv/aleksis/envs/production/lib/python3.9/site-packages/dynamic_preferences/models.py", line 59, in get_value
    return self.preference.serializer.deserialize(self.raw_value)
AttributeError: 'PersonPreferenceModel' object has no attribute 'preference'

That's the way it works:

# Generated by Django 3.2.11 on 2022-01-27 18:52

from email.headerregistry import Group
from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('sites', '0002_alter_domain_unique'),
        ('core', '0034_invite_permission'),
    ]

    def _migrate_preference_models_to_unique(apps, schema_editor):
        from aleksis.core.models import GroupPreferenceModel, PersonPreferenceModel, SitePreferenceModel

        models = [GroupPreferenceModel, PersonPreferenceModel, SitePreferenceModel]

        for model in models:
            duplicates = {}
            db_alias = schema_editor.connection.alias
            for obj in model.objects.using(db_alias).all():
                key = f"{obj.instance.pk}__{obj.section}__{obj.name}"
                duplicates.setdefault(key, [])
                duplicates[key].append(obj)

            for key, objs in duplicates.items():
                if len(objs) > 1:
                    found = False
                    for obj in objs:
                        if obj.value == obj.preference.default or found:
                            obj.delete()
                        else:
                            found = True


    operations = [
        migrations.RunPython(_migrate_preference_models_to_unique),
        migrations.AlterUniqueTogether(
            name='grouppreferencemodel',
            unique_together={('instance', 'section', 'name')},
        ),
        migrations.AlterUniqueTogether(
            name='personpreferencemodel',
            unique_together={('instance', 'section', 'name')},
        ),
        migrations.AlterUniqueTogether(
            name='sitepreferencemodel',
            unique_together={('instance', 'section', 'name')},
        ),
    ]