附加组合SEG故障

我正在尝试根据 Apple's instructions 但一旦我尝试得到 outputImage 从ciadditioncompositing过滤器中,我得到一个SEG错误。这是我在uiimage上用作扩展名的代码。我做错了什么?

public func tiltShift() -> UIImage? {
    guard let backingCi = ciImage ?? CIImage(image: self) else {
        return nil
    }

    let blurred = backingCi.applyingGaussianBlur(sigma: 10)

    var gradientParameters = [
        "inputPoint0": CIVector(x: 0, y: 0.75 * size.height),
        "inputColor0": CIColor(red: 0, green: 1, blue: 0, alpha: 1),
        "inputPoint1": CIVector(x: 0, y: 0.5 * 10),
        "inputColor1": CIColor(red: 0, green: 1, blue: 0, alpha: 0)
    ];

    guard let inputGradient = CIFilter(name: "CILinearGradient", parameters: gradientParameters),
        let inputImage = inputGradient.outputImage else {
            return nil
    }

    gradientParameters["inputPoint0"] = CIVector(x: 0, y: 0.25 * size.height)

    guard let backgroundGradient = CIFilter(name: "CILinearGradient", parameters: gradientParameters),
        let backgroundImage = backgroundGradient.outputImage else {
            return nil
    }

    let maskParameters = [
        "inputImage": inputImage,
        "inputBackgroundImage": backgroundImage
    ]

    guard let mask = CIFilter(name: "CIAdditionCompositing", parameters: maskParameters),
        let maskedImage = mask.outputImage else {  // <=- This line aborts
            return nil
    }

    let combinedParameters = [
        "inputImage": blurred,
        "inputBackgroundImage": self,
        "inputMaskImage": maskedImage
    ]

    guard let blend = CIFilter(name: "CIBlendWithMask", parameters: combinedParameters) else {
        return nil
    }

    let context = CIContext(options: nil)

    guard let blendImg = blend.outputImage,
        let cgimg = context.createCGImage(blendImg, from: blendImg.extent) else { return nil }

    return UIImage(cgImage: cgimg)
}