fix: improve handling deleted GH users

[caugner]

Prevents the following TypeError with events of deleted users (aka "ghost"):

  File "/path/to/github3/models.py", line 52, in __init__
    self._update_attributes(json)
  File "/path/to/github3/issues/event.py", line 63, in _update_attributes
    self.actor = users.ShortUser(event["actor"], self)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/github3/models.py", line 52, in __init__
    self._update_attributes(json)
  File "/path/to/github3/users.py", line 309, in _update_attributes
    self.avatar_url = user["avatar_url"]

TypeError: 'NoneType' object is not subscriptable

Fixes #988.

Version Information

Please provide:

• The version of Python you're using: 3.11.5
• The version of pip you used to install github3.py: 23.2.1
• The version of github3.py (4.0.1), requests (2.31.0), uritemplate (?), and dateutil (?) installed:

Minimum Reproducible Example

n/a

Exception information

n/a

[caugner]

Hi @sigmavirus24, could you please approve the workflows? 🙏

[sigmavirus24]

This won't default to None of I remember correctly. People will instead have an Attribute Error trying to access something that otherwise is there

[caugner]

This won't default to None of I remember correctly. People will instead have an Attribute Error trying to access something that otherwise is there

I'm not sure I understand. Are you saying that this won't help, because people will get a different Error when accessing a property on event.actor without checking event.actor first? I would argue this is still better than before, because users currently cannot do anything against github3 running into this TypeError as soon as they encounter an event by a deleted user (except monkey-patching maybe).

I guess an alternative would be to initialize a GhostUser object instead, as if https://github.com/ghost was a real user.

PS: The failing Python 3.9/3.10 tests seem unrelated.

[sigmavirus24]

I guess an alternative would be to initialize a GhostUser object instead, as if https://github.com/ghost was a real user.

The more I think about it, the more I like the idea of a GhostUser object or a Ghost sentinel that we can return.

[sigmavirus24]

@caugner are you still interested in implementing a GhostUser?