Catalog._cmp_ function needed to cater for None object

[hoangduytran]

Describe the bug

When running dill to detect any bad items for pickle, dill returns error on this function, when trying to compare with a None object.

How to Reproduce

run pip3 install dill

then do

import dill
from sphinx_intl import catalog as c

dill.detect.trace(True)
po_path = <path to po file>
cat: Catalog = c.load_po(po_path)
dill.detect.baditems(cat)

it will say something like this:

File "../lib/python3.9/site-packages/babel/messages/catalog.py", line 169, in values_to_compare
return obj.id, obj.context or ''
AttributeError: 'NoneType' object has no attribute 'id'

if you correct this function by doing this:

def values_to_compare(obj):
            is_none = (obj is None)
            if is_none: # adding blank key for None type object
                return ('', '')

            # print(f'values_to_compare obj:{obj}')
            if isinstance(obj, Message) and obj.pluralizable:
                return obj.id[0], obj.context or ''

            return obj.id, obj.context or ''

then it works

Environment Information

sphinx==7.2.6

# Sphinx dependencies that are important
Jinja2==3.1.2
Pygments==2.16.1
docutils==0.18.1
snowballstemmer==2.2.0
babel==2.13.0
requests==2.31.0

# Only needed for building translations.
sphinx-intl==2.1.0

# Only needed to match the theme used for the official documentation.
# Without this theme, the default theme will be used.
sphinx_rtd_theme==2.0.0rc4

# Only for convenience, allows live updating while editing RST files.
# Access by running:
#   make livehtml
sphinx-autobuild==2021.3.14

# Required for spell-checking
pyenchant

Sphinx extensions

No response

Additional context

No response

[jayaddison]

Thanks for the bugreport @hoangduytran. Are you able to determine how/where these non-picklable catalog items were created?