Make Guild.member_count Optional

[AbstractUmbra]

Summary

According to multiple reports, this key is not always present in a guild payload. Currently the library only sets this attribute if it is not None resulting in a rare error during startup or when retrieving guilds.
Potentially a fix for #6652?

I have made this attribute and property Optional as a result, to avoid an AttributeError.

Sadly I cannot test this, due to potentially requiring an "unavailable" guild.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[Rapptz]

I don't know how I feel about the type of member_count changing to Optional[int]. Python ergonomics with optional types is subpar, especially when the data is always there. Not sure what the solution is but it is unfortunate.

[dolfies]

Unless I'm misremembering, the only time member_count will not be present is when a guild is unavailable. In that case, can't we just default to 0? You could argue it actually is 0 since no-one can access it.

[EvieePy]

I don't think 0 makes a lot of sense here. The guild member count is still above 0, regardless of whether it is unavailable or not.
If you were going to return 0 you might as well just return None for some sanity. But I'm not sure... So goodlock with this.

[dolfies]

None will make typing UX not amazing.

[AbstractUmbra]

I am aware that marking this attribute as Optional is a far from ideal solution, however I believe that it's the lesser of two evils, considering the other option (at the moment) is a rare AttributeError that's been affecting people.

I'd rather a little extra work to appease a type checker than it just dying, personally.

[Rapptz]

Needs updating migrating.rst

[dolfies]

I am aware that marking this attribute as Optional is a far from ideal solution, however I believe that it's the lesser of two evils, considering the other option (at the moment) is a rare AttributeError that's been affecting people.

I'd rather a little extra work to appease a type checker than it just dying, personally.

That's why 0 is a good middle ground. In the rare event it isn't provided, it being 0 shouldn't be a problem. Even name defaults to an empty string.