Support for Optional[...] in CommandArg

[Sigmanificient]

trying to use
CommandArg[Optional[str], Description["..."]] = None
raises

Traceback (most recent call last):
  File "/home/sigmanificient/PycharmProjects/Pincers/Pincer/dev/context.py", line 8, in <module>
    class Bot(Client):
  File "/home/sigmanificient/PycharmProjects/Pincers/Pincer/dev/context.py", line 10, in Bot
    async def a_command(
  File "/home/sigmanificient/PycharmProjects/Pincers/Pincer/pincer/commands/commands.py", line 237, in command
    command_type = _options_type_link[annotation.command_type]
KeyError: typing.Union[str, **NoneType]

the "working" way to do it is the following:

    async def a_command(
        self,
        ctx: MessageContext,
        content: CommandArg[str, Description["..."]] = None,
    ) -> Embed:

But this doesnt seems really fine as None doesn't seems to be typed.
The first argument should be Optional[str]

[ooliver1]

#480 the fixes part (of course) did not link and close this issue properly.