In 0124, when using PImage.save() without using createImage(), I expect
this error:

java.lang.RuntimeException: java.lang.RuntimeException: PImage.save()
requires an absolute path. Or you can use createImage() instead or pass
savePath() to save().

But, I'm getting the error even when using createImage(). Here's a minimal
example:

PImage img;

void setup() {
size(600, 400);
img = createImage(300, 180, RGB);
noLoop();
}

void draw() {
background(102);
img = get(120, 200, img.width, img.height);
img.save("snapshot-####.png");
}

fixed for 0125. get(x, y, w, h) just wasn't setting the parent properly.

in your example, createImage() does nothing because the image created is
cleared out when you say "img =" something else.