Thread 1: [<EggTimer.ViewController 0x7f9788e0c730> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key hardnessSelected. code example

Example: uncaught exception 'NSUnknownKeyException', reason: '[ setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key

//Go to this link :)
//https://stackoverflow.com/questions/38308329/swift-setvalueforundefinedkey-this-class-is-not-key-value-coding-compliant-f