I understand that piece that I should try to find what is null in the code myself, but from my knowledge nothing is null at the moment, nor should it be null because the only code running in that script is from the forum post you provided:
This is the step that it is failing on.
ImageIO.write(saveImage, "png", new File("C:\\test\\test-image.png"))
It should be providing all parameters for that from what I understand, but I’m still getting an NPE