问Swift:如何理解下载的镜像是空的？

EN

func downloadFrom(link: String, contentMode mode: UIView.ContentMode = .scaleAspectFit, rounded: Bool = false, loader: IndicatorType = .none) {
        self.kf.indicatorType = loader
        guard let url = URL(string: link) else {
            return
        }
        let img = self.image

        if(rounded) {
            let roundedProcessor = RoundCornerImageProcessor(cornerRadius: 100, targetSize: CGSize(width: 200, height: 200), roundingCorners: .all, backgroundColor: nil)
            self.kf.setImage(with: url, placeholder: img, options: [.processor(roundedProcessor)], completionHandler: {
                (image, error, cacheType, imageUrl) in

                if (error == nil) {
                    DispatchQueue.main.async() { () -> Void in
                        if (self.contentMode != UIView.ContentMode.scaleAspectFit) {
                            self.contentMode = mode
                        }
                    }
                }
            })
        } else {
            self.kf.setImage(with: url, placeholder: img, completionHandler: {
                (image, error, cacheType, imageUrl) in

                if (error == nil) {
                    DispatchQueue.main.async() { () -> Void in
                        if (self.contentMode != UIView.ContentMode.scaleAspectFit) {
                            self.contentMode = mode
                        }
                    }
                }
            })
        }
    }