PVector angleBetween returns 0 when x and y of either parameter are both 0

I found an existing report describing similar behavior with 3D PVectors (https://github.com/processing/processing/issues/2045), but it appears the same problem affects 2D PVectors as well.

When either the start or end PVector is (0,0) the output of angleBetween() is always 0.

I'm not particularly experienced with Processing, so it's entirely possible that I'm misunderstanding something or using the API incorrectly. I tend to pick it up every few months for small projects and then promptly forget most of what I learned.

That said, I've spent some time testing this behavior and looking into the implementation, and based on what I found, I would not expect the angle to be 0 in the cases I tested.

Edit: I forgot to add, I'm using processing 4.5.2

Start at the PVector.angleBetween() entry point and compare the 2D behavior with the related 3D report in issue #2045. Clarify the expected result when either vector is (0,0), then verify the corrected behavior with regression coverage for those cases.