Type of expression is ambiguous without more context

Hello fellow developers, I'm porting the screenshot logic for WKWebView at https://github.com/VernonVan/PPSnapshotKit/blob/master/PPSnapshotKit/Source/PPSnapshotHandler.m#L95 from Objective-C to Swift and faced a cryptic error.

FYI, Xcode 12.4 and Build version 12D4e.

            let view = self.flutterWebView?.view()
            let webView = self.flutterWebView!.webView;
            let snapshotView = webView!.snapshotView(afterScreenUpdates: true);
            webView!.superview!.addSubview(snapshotView!)

            let currentOffset = webView!.scrollView.contentOffset
            let currentFrame = webView!.frame
            let currentSuperView = webView!.superview
            var currentIndex = webView!.superview!.subviews.firstIndex(of: webView!)

            let containerView = UIView(frame: webView!.bounds)
            webView!.removeFromSuperview()
            containerView.addSubview(webView!)
    
            let totalSize = webView!.scrollView.contentSize
            let page = ceil(totalSize.height  / containerView.bounds.size.height)

            webView!.scrollView.contentOffset = .zero;
            webView!.frame = CGRect(0, 0, containerView.bounds.size.width, webView!.scrollView.contentSize.height);

            UIGraphicsBeginImageContextWithOptions(totalSize, true, 0)
            
            self.drawContentPage(targetView: containerView, webView: webView, index: 0, maxIndex: page) {
                let snapshotImage = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsGetImageFromCurrentImageContext()
                
                webView?.removeFromSuperview()
                currentSuperView?.insertSubview(webView, at: currentIndex)
                webView?.frame = currentFrame
                webView?.scrollView.contentOffset = currentOffset
                snapshotView?.removeFromSuperview()
                return result(snapshotImage?.pngData())
            }

    public func drawContentPage(targetView: UIView, webView: WKWebView, index: Int = 0, maxIndex: Int,  completion: () -> Void) {
        let splitFrame = CGRect.init(0, CGFloat(index) * targetView.bounds.height, targetView.bounds.size.width, targetView.frame.size.height)
        var myFrame = webView.frame
        myFrame.origin.y -= (CGFloat(index) * targetView.frame.size.height)
        webView.frame = myFrame
        
        DispatchQueue.main.asyncAfter(deadline: .now() + (DELAY_TIME_DRAW * Double(NSEC_PER_SEC))) {
            targetView.drawHierarchy(in: splitFrame, afterScreenUpdates: true)
            if (index < maxIndex) {
                self.drawContentPage(targetView: targetView, webView: webView, maxIndex: maxIndex, completion: completion)
            }
            else {
                completion()
            }
        }
    }