Editing Photo metadata and PHAdjustmentData - ios

Question

The following function loads a photo, edits the exif metadata attached to it and saves it back out. The function only seems to work for photos that already have a PHAdjustmentData attached ie photos that have been edited with another application previously. If a photo hasn't been edited it fails in the performChanges() block and prints
Failed to save. Error: Optional(Error Domain=NSCocoaErrorDomain Code=-1 "(null)").
Why does it fail in this situation? Looking through Stack Overflow I have seen a number of other versions of this question but none of them seemed to get resolved. I know this fails if the image saved is a PNG but my original image is a JPEG so the saved image is also a JPEG.
func editPhotoProperties(_ asset: PHAsset) {
let options = PHContentEditingInputRequestOptions()
options.canHandleAdjustmentData = { data in
return false
}
asset.requestContentEditingInput(with: options) { input, info in
if let input = input {
let adjustmentData = PHAdjustmentData(formatIdentifier:"viewfinder", formatVersion:"1.0", data:"viewfinder".data(using:.utf8)!)
let output = PHContentEditingOutput(contentEditingInput:input)
output.adjustmentData = adjustmentData
do {
let imageData = try Data(contentsOf:input.fullSizeImageURL!)
} catch {
print("Failed to load data")
return
}
let properties = getImageDataProperties(imageData)!
let properties2 = properties.mutableCopy() as! NSMutableDictionary
// edit properties2
...
let newImageData = addImageProperties(imageData: imageData, properties: properties2)
do {
try newImageData!.write(to: output.renderedContentURL, options: .atomic)
} catch {
print("Failed to write to disk")
return
}
PHPhotoLibrary.shared().performChanges({
let changeRequest = PHAssetChangeRequest(for:asset)
changeRequest.contentEditingOutput = output
}) { success, error in
if !success {
print("Failed to save. Error: \(String(describing:error))")
}
}
}
}
}
func getImageDataProperties(_ data: Data) -> NSDictionary? {
if let imageSource = CGImageSourceCreateWithData(data as CFData, nil) {
if let dictionary = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) {
return dictionary
}
}
return nil
}
// add image properties (exif, gps etc) to image
func addImageProperties(imageData: Data, properties: NSDictionary?) -> Data? {
// create an imagesourceref
if let source = CGImageSourceCreateWithData(imageData as CFData, nil) {
// this is of type image
if let uti = CGImageSourceGetType(source) {
// create a new data object and write the new image into it
let destinationData = NSMutableData()
if let destination = CGImageDestinationCreateWithData(destinationData, uti, 1, nil) {
// add the image contained in the image source to the destination, overidding the old metadata with our modified metadata
CGImageDestinationAddImageFromSource(destination, source, 0, properties)
if CGImageDestinationFinalize(destination) == false {
return nil
}
return destinationData as Data
}
}
}
return nil
}