Allow kicking user from voice channels with `Server.move` by passing `nil` for `channel_id`

[gregdan3]

Discord.js and discordpy both support this feature by passing their equivalent of nil:

• https://discordpy.readthedocs.io/en/latest/api.html#discord.Member.move_to
• https://discord.js.org/#/docs/discord.js/main/class/VoiceState?scrollTo=setChannel

discordrb's equivalent, Server.move, evaluates the channel's ID and fails if nil is passed.

• https://drb.shardlab.dev/v3.4.2/Discordrb/Server.html#move-instance_method

Admittedly, I don't immediately see how this is possible via the API, as the modify user voice state endpoint doesn't allow for a null channel id.

https://discord.com/developers/docs/resources/guild#modify-current-user-voice-state

Still, given this is implemented in two other libraries, it must be possible.

[Sobsz]

Confusingly, the relevant request is actually Modify Guild Member, as Modify User Voice State is stated to only work on stage channels. The former's documentation states:

If the channel_id is set to null, this will force the target user to be disconnected from voice.

[swarley]

Howdy, you've identified an issue that we've been living with for a while due to some poor design in our API handler that the rest of the library depends on.

Basically, we don't have a way to send a null value to the HTTP API because we compact out null values just before sending the request.

I'm going to look into a workaround to make this sort of thing possible in v3 before we switch to work on v4

[Dakurei]

I randomly found this, and in fact it's easily possible since the acceptance of PR #113

It's been a while since the method no longer deletes values at nil, but as it was on the v3.4.2 gem doc, and not the 'main' branch one (as the issue link suggests), it wasn't noticed.

All it takes is one character to solve the problem 🤣

I can send a quick PR if needed 👍