Error when try to delete a channel from an account [standalone thingspeak server] | GitHub Installation | Forum

Good day, everyone. I've managed to setup a standalone server for thingspeak (https://github.com/other/thingspeak). Unfortunately, I've found an error in the ruby on rails code shown in the attachments. The problem occur whenever i tried to remove a channel using the "delete channel" button on the channel's setting page. Therefore, i would like to ask if anyone already have a fix for this error and please guide me to solve the problem. Your cooperation is truly appreciated.