Branch provisioning can fail if stale content types are present

[jeremystretch]

Plugin Version

0.6.0

NetBox Version

4.3.3

Python Version

3.10

Steps to Reproduce

1. Load the v4.3 NetBox demo data
2. Enable the plugin & apply migrations
3. Start an RQ worker process
4. Attempt to provision a branch

Expected Behavior

The branch should provision successfully

Observed Behavior

An AttributeError exception is raised:

AttributeError: 'NoneType' object has no attribute '_meta'

This is due to a stale ContentType for the ContactGroupMembership model. Running the management command manage.py remove_stale_contenttypes to remove it resolves the error. However, we should also account for such issues when discovering relevant models.