That is because this API endpoint is for the stream object only - if you want channel information then you can use the endpoint:
https://api.twitch.tv/kraken/channels/CHANNELHERE?client_id=clientIDHere
Closed/Banned accounts, I believe, will always return:
{"error":"Unprocessable Entity","status":422,"message":"Channel 'USERNAME is unavailable"}
Also, a heads up for the future, probably best to not necro a 2 year old thread - would be better off to start a new one with your own question, since it appears you are looking for something different than OP 