_pickle.UnpicklingError after failed migration

[Adam01]

Describe the problem

Migrations containing 0003_drop_pickle often fail. I recently noticed this happens when 0003 succeeds in a migration where another migration has failed, and running the migration again after fixing the other migration leads to this error.

Steps to reproduce

Migrate to 0003_drop_pickle after a previous call to migrate failed where 0003 succeeded in that migration.

System configuration

• Django version: 5.1.1
• Python version: 3.12
• Django-Constance version: 4.1.1

Last line of stack trace

  File "/app/.heroku/python/lib/python3.12/site-packages/django/db/migrations/migration.py", line 132, in apply
    operation.database_forwards(
  File "/app/.heroku/python/lib/python3.12/site-packages/django/db/migrations/operations/special.py", line 196, in database_forwards
    self.code(from_state.apps, schema_editor)
  File "/app/.heroku/python/lib/python3.12/site-packages/constance/migrations/0003_drop_pickle.py", line 23, in migrate_pickled_data
    constance.value = dumps(pickle.loads(b64decode(constance.value.encode())))  # noqa: S301
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_pickle.UnpicklingError: invalid load key, '\xb7'.
Django migrations failed

Constance table 'value' column values

1. {"type": "default", "value": ""}
2. gAJHP564UeuFHrgu

Workaround

Delete records with 'value' column containing JSON