django-DefectDojo: Unable to serialize database with dumpdata

Bug description On a python3 dev branch (from june 26), I wanted to perform a dumpdata prior to upgrading. The following command

docker exec -ti dojo_upstream_afterpy3_migration_uwsgi_1 bash -c 'python manage.py dumpdata --indent=4 -e sessions -e admin --natural-foreign --natural-primary -e contenttypes -e auth.permission' > datadump_prior_to_update.json

launches, performs up to a certain point before failing with this error:

CommandError: Unable to serialize database: 'MultiSelectField' object has no attribute '_get_val_from_obj'
}Exception ignored in: <generator object cursor_iter at 0x7f6ba391f660>
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/django/db/models/sql/compiler.py", line 1515, in cursor_iter
    cursor.close()
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/cursors.py", line 86, in close
    while self.nextset():
  File "/usr/local/lib/python3.7/site-packages/MySQLdb/cursors.py", line 136, in nextset
    nr = db.next_result()
MySQLdb._exceptions.OperationalError: (2006, '')

Expected behavior The dumpdata works.

Deployment method (select with an X)

• Kubernetes
• Docker
• setup.bash / legacy-setup.bash