title: No '+' candidates produce the expected contextual result type 'NSNumber?' Swift 3
body: <p>On Xcode 8 and Swift 3 is comes an error by + i have try it anything but come to no result. 
  Here the code : </p>
  
  <pre><code>static func addNotificationInterval(title: String, body: String,
  
  indentifier: String, interval: Double) {
  
      let content = UNMutableNotificationContent()
      content.title = NSString.localizedUserNotificationString(forKey: title, arguments: nil)
      content.body = NSString.localizedUserNotificationString(forKey: body, arguments: nil)
      content.sound = UNNotificationSound.default()
      content.badge = UIApplication.shared.applicationIconBadgeNumber + 1; content.categoryIdentifier = "com.elonchan.localNotification"
  
      let trigger = UNTimeIntervalNotificationTrigger.init(timeInterval: interval, repeats: true)
      let request = UNNotificationRequest.init(identifier: indentifier, content: content, trigger: trigger)
      let center = UNUserNotificationCenter.current()
  
      center.add(request)
  
      print("SetNotifiInterval")
  
  }
  </code></pre>
  
  <p>Error comes here by the + : </p>
  
  <pre><code>content.badge = UIApplication.shared.applicationIconBadgeNumber + 1; content.categoryIdentifier = "com.elonchan.localNotification"
  </code></pre>
  
  <p>Error Type: </p>
  
  <p>No '+' candidates produce the expected contextual result type 'NSNumber?'</p>