Converting UIImage to CIImage Returns nil - swift

Question

I'm trying to convert the UIImage from an imageView into a CIImage for the purpose of filtering it. However, I cannot get the CIImage to have a value.
In the simplest form, here's what I am trying:
let ciInput = CIImage(image: imageView.image!)
but the ciInput always is nil.
I have also tried
let ciInput = CIImage(cgImage: imageView.image!.cgImage)
but also returns nil.
(imageView.image is not nil, but imageView.image!.cgImage and imageView.image!.ciImage are both nil)
I need to convert the UIImage from the imageView into a valid CIImage. Any help is appreciated, thanks!
EDIT: Here is the full function code
func makeWhiteTransparent(imageView: UIImageView) {
let invertFilter = CIFilter(name: "CIColorInvert")
let ciContext = CIContext(options: nil)
let ciInput = CIImage(image: imageView.image!) //This is nil
invertFilter?.setValue(ciInput, forKey: "inputImage")
let ciOutput = invertFilter?.outputImage
let cgImage = ciContext.createCGImage(ciOutput!, from: (ciOutput?.extent)!)
imageView.image = UIImage(cgImage: cgImage!)
}
When running this function, I get a fatal unwrapping nil error on the last line. Using the debugger, I discovered that the ciInput is nil, which it should not be.
EDIT 2:
The image on the imageView before calling makeWhiteTransparent is a QR code generated with this function:
func generateQRCode(from string: String) -> UIImage? {
let data = string.data(using: String.Encoding.ascii)
if let filter = CIFilter(name: "CIQRCodeGenerator") {
filter.setValue(data, forKey: "inputMessage")
let transform = CGAffineTransform(scaleX: 12, y: 12)
if let output = filter.outputImage?.applying(transform) {
return UIImage(ciImage: output)
}
}
return nil
}

Answer 1

So the problem was in my QR Code generation. The code returned a UIImage from a CIImage without properly utilizing CGContext to return the UIImage. Here is the corrected QR Code function that fixed the issue.
func generateQRCode(from string: String) -> UIImage? {
let data = string.data(using: String.Encoding.ascii)
if let filter = CIFilter(name: "CIQRCodeGenerator") {
filter.setValue(data, forKey: "inputMessage")
let transform = CGAffineTransform(scaleX: 12, y: 12)
if let output = filter.outputImage?.applying(transform) {
let context = CIContext()
let cgImage = context.createCGImage(output, from: output.extent)
return UIImage(cgImage: cgImage!)
}
}
return nil
}