Getting nil while unwrapping an optional value error - while saving enum value in Swift

Question

I have the following event model:

class Event: NSObject, NSCoding {

  var name: String
  var category: Category

  enum Category: String {
    case Call = "Call"
    case Coaching = "Coaching"
  }
}

When a user updates their selection of the category enum it crashes with the error: fatal error: unexpectedly found nil while unwrapping an Optional value. However when I print "selected category" I get the correct response: "Call."

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
  if saveButton === sender {
    let name = eventNameTextField.text ?? ""
    let category = eventCategoryLabel.text!

    if let cat = Event.Category(rawValue:category) {
      print("selected category: \(cat)")
      event = Event(name: name, category: cat)
    }    
  }
}

Am I missing something when it comes to saving selecting strings as enum options? Thanks in advance for everyone's time!