[VoiceStateUpdate] oldState.channelId return null

[002-sans]

I just got a probleme, I wanna do some "tempvoc" system and got a problem. Sometimes oldState.channelId == null (when I disconnect the channel) and when I move to another channel, oldState.channelId == "ChannelID". That's strange bcs my code is very simple and that's not an error from me (I guess).

// Just a code for example
if (oldState && oldState.guild){
    console.log(oldState.channelId);
}