Django Admin - 500 error on saving any DB record without making changes

[rnovak338]

Describe the bug

LogEntry expects changes to be recorded when you edit a DB entry in Django Admin. It parses a JSON snippet during this event.
However, if a record is "updated" but no changes to the fields are made, this JSON changelog snippet is empty while the logic for LogEntry is still expecting there to be JSON to work with. This leads to a 500 error.

Steps to reproduce the bug

1. Log into the admin panel.
2. Make changes to an editable record.
3. Attempt to save - you should experience a 500 crash.

Expected Behavior

The changes should save successfully, and a LogEntry should be created with no JSON, indicating that no changes were actually made.

Code of Conduct

• I agree to abide by the Digital.gov Community Guidelines and the TTS Code of Conduct. Respect your peers, use plain language, and be patient.
• I checked the current issues for duplicate bug reports.