One of many Photos.framework idiosyncrasies

LoadThumbnail.swift

    /*
     If you run loadThumbnail() in an *iPhone-only app that is installed on the iPad*,
     the Photos framework will callback first with a degraded version of the requested asset image,
     and then it will callback a second time with a nil image. 
     
     If you're not careful and you pass the nil image to your UIImageView, then you will never see the thumbnail.
     The UIImageView will first get set with a proper UIImage, then soon after with a nil UIImage.
     The solution is to ignore or discard any image that is nil.
     
     So what happens if you try to setup PHImageRequestOptions to make sure that Photos framework only calls back once?
     You do get only one callback then, except it's always with a nil image.
     */
    func loadThumbnail(asset: PHAsset, targetSize: CGSize, completion: (Result<UIImage, NSError> -> Void)) {
        let emptyOptions = PHImageRequestOptions()
        PHImageManager.defaultManager().requestImageForAsset(asset, targetSize: targetSize, contentMode: .AspectFill, options: emptyOptions) { image, dictionary in
            if let image = image {
                completion(Result(value: image))
            } else {
                let error = NSError(domain: "com.example.domain", code: 0, userInfo: [NSLocalizedDescriptionKey: "Example localized description."])
                completion(Result(error: error))
            }
        }
    }