Mailgun webhooks: AttributeError 'NoneType' object has no attribute 'get'

[izimobil]

In certain cases delivery-status can be None in the event POST data sent to the webhook.
Anymail does not handle this case and throws an AttributeError.

• Anymail version: 9.1
• ESP (Mailgun, SendGrid, etc.): mailgun
• Versions of Django, requests, python:

Django 3.2
Requests 2.31.0
Python 3.11

• Exact error message and/or stack trace

AttributeError
       at /anymail/mailgun/tracking/
'NoneType' object has no attribute 'get'
  
Request Method: | POST
https://redacted.org/anymail/mailgun/tracking/
3.2
AttributeError
'NoneType' object has no attribute 'get'
/home/redacted/VirtualEnvs/redacted.org/lib/python3.9/site-packages/anymail/webhooks/mailgun.py, line 179, in esp_to_anymail_event

[medmunds]

(Fix released in Anymail 10.3)