Attachment.content_type can be None, but there are some places where we assume it is a string:

• bot/bot/exts/filtering/filtering.py

  Line 238 in f0e4d45

  for a in msg.attachments if "charset" in a.content_type

• bot/bot/exts/utils/attachment_pastebin_uploader.py

  Line 81 in f0e4d45

  if message.author.bot or not any("charset" in a.content_type for a in message.attachments):

• bot/bot/exts/utils/attachment_pastebin_uploader.py

  Line 112 in f0e4d45

  if "charset" in f.content_type

This has come up in production BOT-3ZJ, BOT-3ZH, and BOT-42E.

I assume the fix is as simple as ignoring None values, but I haven't looked into the code here.