None check for check_guilds

[freemanovec]

Summary

check_guilds has been marked as optional, but no None check was being done causing TypeError: unsupported operand type(s) for +: 'bool' and 'list' when passing None to check_guilds

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why
• 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, typehinting, examples, ...)

[Lulalaby]

@krittick what do you think.
What we gonna do with this?