Removing a plugin can cause exceptions when viewing change records

[jeremystretch]

NetBox version

v3.1.6

Python version

3.8

Steps to Reproduce

1. Install a plugin
2. Create an instance of a model provided by the plugin, resulting in the creation of a changelog entry
3. Uninstall the plugin
4. View the changelog

This has come up a few times in discussion. One recent example can be found in #8418.

Expected Behavior

The changelog should render successfully.

Observed Behavior

An exception is raised when the changelog entry relevant to the plugin model is present:

<class 'AttributeError'>

'NoneType' object has no attribute '_base_manager'

[jeremystretch]

@DanSheps have you made any progress on this?

[DanSheps]

@jeremystretch I think I captured all locations where this might pop up.