Saving to User Photo Library Silently Fails

I was trying to save an image to the user camera roll on my iPhone using this code:

UIImageWriteToSavedPhotosAlbum(uiImage, nil, nil, nil)

But despite not crashing or giving an error, it was failing. I made sure the image was a valid (not nil) UIImage, and it was. So then I tried implementing the completion handler like so:

UIImageWriteToSavedPhotosAlbum(uiImage, self, #selector(self.image(_:didFinishSavingWithError:contextInfo:)), nil)

// ....

@objc func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: UnsafeRawPointer) {
    if error != nil {
        print("ERROR! ", error!.localizedDescription)
    }
}

But this still didn't give me an error. Finally, I tried running on the simulator. This then gave me the following errors:

Connection to assetsd was interrupted or assetsd died

Error! Write failed

What is causing this to fail?