As of very recent, some Discord.js users are now running into these errors:
guild.channels.set(channel.id, channel);
^
TypeError: Cannot read property 'id' of undefined
bughunter Bug:
node_modules\discord.js\src\client\voice\networking\VoiceWebSocket.js:123
server_id: this.connection.channel.guild.id,
^
TypeError: Cannot read property 'guild' of undefined
Read the provided answer below.