TypeError: 'NoneType' object is not iterable

[Renkineko]

Hi.

I'm trying to use MPTT with parler to translate my website, more exactly the FAQ on it. The models are quite simples, but I didn't manage to succeed to configure it without django-categories-i18n. Google is failing me, Django copilot also... So I'm opening this issue, sorry about that.

Here are my models:

from django.db import models
from mptt.models import TreeManyToManyField
from parler.models import TranslatableModel, TranslatedFields
from django.utils.translation import gettext_lazy
from categories_i18n.models import Category as BaseCategoryI18n

from martor.models import MartorField

class CategoryI18n(BaseCategoryI18n):
    css_classes = models.CharField(gettext_lazy("classes CSS"), max_length=256, blank=True)
    
class QuestionI18n(TranslatableModel):
    SRC_DISCORD = 'discord'
    SRC_FACEBOOK = 'facebook'
    SRC_FORUM = 'forum'
    SRC_MAIL = 'mail'
    SRC_PDF = 'pdf'
    source_type_choices = (
        (SRC_PDF, gettext_lazy('FAQ PDF')),
        (SRC_FORUM, gettext_lazy('Forum')),
        (SRC_DISCORD, gettext_lazy('Discord')),
        (SRC_FACEBOOK, gettext_lazy('Facebook')),
        (SRC_MAIL, gettext_lazy('Mail')),
    )
    
    TranslatedFields(
        question = models.CharField(gettext_lazy("question"), max_length=512),
        answer = MartorField(gettext_lazy("answer"), blank=True, null=True),
        source_type = models.CharField(gettext_lazy('source type'), max_length=8, choices=source_type_choices, blank=True, null=True),
    )
    gm = models.BooleanField(gettext_lazy('filtre MJ'), blank=True, default=False)
    v1 = models.BooleanField(gettext_lazy('compatible v1'), blank=True, default=True)
    v1_5 = models.BooleanField(gettext_lazy('compatible v1.5'), blank=True, default=True)
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)
    category = TreeManyToManyField(
        CategoryI18n,
        verbose_name=gettext_lazy("catégorie(s)"),
        related_name="questions",
        blank=True
    )

I can create CategoryI18n, no problem here. The problem is when I try to create a question, even without a category (I added the blank=True to see if a question without category would work... The answer is no :( )

In a shell:

from gm.models.faq import QuestionI18n
q = QuestionI18n()
q.question='test'
q.save()

It output this exception:

TypeError                                 Traceback (most recent call last)
Cell In[4], line 1
----> 1 q.save()

File ~/git/knightools/venv/lib/python3.10/site-packages/parler/models.py:717, in TranslatableModelMixin.save(self, *args, **kwargs)
    712 # Makes no sense to add these for translated model
    713 # Even worse: mptt 0.7 injects this parameter when it avoids updating the lft/rgt fields,
    714 # but that misses all the translated fields.
    715 kwargs.pop("update_fields", None)
--> 717 self.save_translations(*args, **kwargs)

File ~/git/knightools/venv/lib/python3.10/site-packages/parler/models.py:759, in TranslatableModelMixin.save_translations(self, *args, **kwargs)
    756 # Copy cache, new objects (e.g. fallbacks) might be fetched if users override save_translation()
    757 # Not looping over the cache, but using _parler_meta so the translations are processed in the order of inheritance.
    758 local_caches = self._translations_cache.copy()
--> 759 for meta in self._parler_meta:
    760     local_cache = local_caches[meta.model]
    761     translations = list(local_cache.values())

TypeError: 'NoneType' object is not iterable

It occurs too deeply for my knowledge and thus I have no idea about how to workaround this problem.

Python 3.10.12
Django 5.1.1
django-categories-i18n 2.0
django-mptt 0.16.0
django-parler 2.3

Any clue? I'm beginning to think I will have to duplicate all my databases and have multiple instances of my project running, one by language... But I would really prefer to make MPTT works (and also rest and elasticsearch, but that I will try once I succeed with MPTT)