Преобразовать ошибку swift 2.3 в swift 3

я конвертирую swift 2.3 в swift 3 в xcode 8.2

swift 2.3: Есть ли код, Есть ли код, Есть ли код, Есть ли код, Есть ли код

func playAudio() {
    self.stopAudio()
    let lessonObject:LessonObject = self.lessonArray[self.selectedIndex] as! LessonObject
    let fullPath:String! = Constants.URL_HOST + "\(lessonObject.lessonPath)"
    let soundURL:NSURL! = NSURL.init(string:fullPath)
    let documentsDirectoryURL =  NSFileManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first!
    let destinationUrl = documentsDirectoryURL.URLByAppendingPathComponent(soundURL.lastPathComponent!)
    if NSFileManager().fileExistsAtPath(destinationUrl!.path!) {
        if let soundData = NSData(contentsOfFile: destinationUrl!.path!) {
            self.initAudioWithData(soundData)
        }
        else {
            self.audioErrorAction()
        }
        return
    }
    
    if let soundData = NSData(contentsOfURL:NSURL(string:fullPath)!) {
        self.initAudioWithData(soundData)
    }
    else {
        self.audioErrorAction()
    }
}

swift 3: Есть ли ошибка в коде?

        func playAudio() {
        self.stopAudio()
        let lessonObject:LessonObject = self.lessonArray[self.selectedIndex] as! LessonObject
        let fullPath:String! = Constants.URL_HOST + "\(lessonObject.lessonPath)"
let soundURL:URL! = URL.init(fileURLWithPath: fullPath)
        let documentsDirectoryURL =  FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
let destinationUrl = documentsDirectoryURL.appendingPathComponent(soundURL.lastPathComponent)
        if FileManager().fileExists(atPath: destinationUrl.path){
            if let soundData = try? Data(contentsOf: URL(fileURLWithPath: destinationUrl.path))
            {
                self.initAudioWithData(soundData)
            }
            else {
                self.audioErrorAction()
            }
            return
        }
if let soundData = try? Data(contentsOf: URL(string:fullPath)!)
        {
            self.initAudioWithData(soundData)
        }
        else {
            self.audioErrorAction()
        }
    }

после преобразования моей ошибки:

найдено nil при развертывании необязательного значения.

Я строю swift 2.3: destinationUrl = file:///Users/admin/Library/.../Documents/test.mp3 0x00006080002a73e0

Я создаю swift 3: destinationUrl = file:///Users/admin/Library/.../Documents/Optional(%22test.mp3%22)