将元数据应用于图像会导致 PerformChanges 请求失败

我正在使用 PhotoKit 编辑照片，并且需要保留原始照片中的元数据。为此，我保存元数据，然后将其提供给options参数输入CGImageDestinationAddImage。我能够完成它并将其成功写入磁盘，但是当我调用performChanges提交资产编辑，失败。如果我改为提供nil for options它会成功的。这里出了什么问题？

asset.requestContentEditingInputWithOptions(options) { (input: PHContentEditingInput!, _) -> Void in
    //get full image
    let url = input.fullSizeImageURL
    let inputImage = CIImage(contentsOfURL: url)

    //get orginal photo's metadata
    let originalImageData = NSData(contentsOfURL: url)!
    let imageSource = CGImageSourceCreateWithData(originalImageData, nil)
    let metadata: CFDictionaryRef = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil)
    println(metadata) //prints all the metadata, yay!

    //do some processing on original photo here and create an output CIImage...

    //save to disk
    let dataRef = CFDataCreateMutable(nil, 0)
    let destination = CGImageDestinationCreateWithData(dataRef, CGImageSourceGetType(imageSource), 1, nil)
    let eaglContext = EAGLContext(API: .OpenGLES2)
    let ciContext = CIContext(EAGLContext: eaglContext)
    let cgImage = ContextStruct.ciContext!.createCGImage(outputPhoto, fromRect: outputPhoto.extent())
    CGImageDestinationAddImage(destination, cgImage, metadata) //metadata is problematic - replacing with nil causes it to work

    if CGImageDestinationFinalize(destination) {
        let contentEditingOutput = PHContentEditingOutput(contentEditingInput: input)
        contentEditingOutput.adjustmentData = "something"

        let imageData: NSData = dataRef
        let success = imageData.writeToURL(contentEditingOutput.renderedContentURL, options: .AtomicWrite, error: _)
        if success {
            PHPhotoLibrary.sharedPhotoLibrary().performChanges({ () -> Void in
                let request = PHAssetChangeRequest(forAsset: asset)
                request.contentEditingOutput = contentEditingOutput
            }, completionHandler: { (success: Bool, error: NSError!) -> Void in
                if success == false { println('failed to commit image edit: \(error)') } //fails unless metadata is replaced with nil above
            })
        }
    }
})

错误是：Error Domain=NSCocoaErrorDomain Code=-1 "The operation couldn’t be completed. (Cocoa error -1.)

看来要填满adjustementData的财产PHContentEditingOutput为了编辑照片，对象是必需的。