How do I save an openJFX11 Canvas as a png/bitmap?

Question

Google is giving me a lot of old results for this (JavaFX). People point you at code using:

RenderedImage, SwingFXUtils and ImageIO

I have openJFX11 and it does not contain these libraries.

How can I save the canvas using built in JFX11 libraries?

My SaveUtil class using old libraries that can't be found:

public void saveCanvas(){


    FileChooser fileChooser = new FileChooser();

    //Set extension filter
    FileChooser.ExtensionFilter extFilter =
            new FileChooser.ExtensionFilter("png files (*.png)", "*.png");
    fileChooser.getExtensionFilters().add(extFilter);

    //Show save file dialog
    File file = fileChooser.showSaveDialog(primaryStage);

    if(file != null){
        try {
            WritableImage writableImage = new WritableImage(CANVAS_WIDTH, CANVAS_HEIGHT);
            canvas.snapshot(null, writableImage);
            RenderedImage renderedImage = SwingFXUtils.fromFXImage(writableImage, null);
            ImageIO.write(renderedImage, "png", file);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}