Partial preserving of Exif does not work of the "Exif" object is not preserved

[dtantsur]

The example in the docs does not actually work:

[2020-12-29 17:52:26] ERROR: render_galleries: Can't process galleries/...., using original image! ('Exif')
Traceback (most recent call last):
  File "/home/dtantsur/.local/lib/python3.8/site-packages/nikola/image_processing.py", line 163, in resize_image
    save_args['exif'] = piexif.dump(exif)
  File "/home/dtantsur/.local/lib/python3.8/site-packages/piexif/_dump.py", line 38, in dump
    exif_ifd = exif_dict["Exif"]
KeyError: 'Exif'

(I've modified the code to output the traceback).

The fix is very simple: change

                    if 'Exif' in exif:
                        exif["Exif"][piexif.ExifIFD.PixelXDimension] = w
                        exif["Exif"][piexif.ExifIFD.PixelYDimension] = h

to

                    if 'Exif' in exif:
                        exif["Exif"][piexif.ExifIFD.PixelXDimension] = w
                        exif["Exif"][piexif.ExifIFD.PixelYDimension] = h
                    else:
                        exif["Exif"] = {}

(I guess the same should be done for 0th).

[dtantsur]

It's more of a bug in piexif: hMatoba/Piexif#114. Keeping this issue open for maintainers to decide if they want to land a workaround.

[Kwpolska]

I believe this should be fixed in piexif.