How to properly use file_raw_save via Python (GIMP PDB Procedure)

While writing a GIMP 2.0 plugin via Python and gimpfu, I've run into pdb procedures such as file_raw_save(...). There arguments are laid out in the GIMP Procedure Browser (Help->Procedure Browser). But when calling them I receive very unhelpful output. My code and output is as follows:

Plugin code:

def save_aci(save_img, filename):
    img = save_img
    filename = filename.strip()
    pdb.file_raw_save(img, img.layers[0], filename, filename)

register(
    "python_fu_save_aci",
    "Exports to ACI file",
    "Exports image to ACI file, with LODs if they are present",
    "Author",
    "Author",
    "2023",
    "Save ACI File",
    "GRAYA",      # Currently only support export from Grayscale image (with alpha) to (RG_88) .aci format
    [
        (PF_IMAGE, "save_img", "Image to Save", None),
        (PF_FILE, "filename", "Filename Fullpath", None),
    ],
    [],
    save_aci, menu="<Image>/File/")

main()

Output when running GIMP plugin:

/home/astro/.gimp-2.8/plug-ins/testplugin.py: fatal error: Segmentation fault
^C/usr/lib64/gimp/2.0/plug-ins/script-fu terminated: Interrupt
gimp: terminated: Interrupt
/home/astro/.gimp-2.8/plug-ins/testplugin.py terminated: Interrupt
/home/astro/.gimp-2.8/plug-ins/testplugin.py terminated: Interrupt
[astro@cobalt-vm plug-ins]$ gimp
Traceback (most recent call last):
  File "/usr/lib64/gimp/2.0/python/gimpfu.py", line 736, in response
    dialog.res = run_script(params)
  File "/usr/lib64/gimp/2.0/python/gimpfu.py", line 361, in run_script
    return apply(function, params)
  File "/home/astro/.gimp-2.8/plug-ins/testplugin.py", line 128, in save_aci
    pdb.file_raw_save(img, img.layers[0], filename, filename)
RuntimeError: calling error

After messing around with the filename arguments (perhaps one expected a path, and the other just a filename), the same output occurs. I was unable to find any documentation on this issue either.

My GIMP version is 2.8 and GIMP is running the script via Python 2.7.

Any suggestions?

Your code is OK and works in Gimp 2.10. I get the same calling error when I run it in my Gimp 2.8. So I assume it's a bug that was fixed later.

Gimp 2.10 has been around for over 5 years, so why Gimp 2.8?