formset error

[hcjohnston]

using djagno 5.0

I have an UpdateView which uses a ModelForm and two formsets ("item_formset" and "section_formset" below) to update a model. Both formsets have extra=0 and no initial data.
I am getting an error when the item_formset.is_valid() is called. see traceback below. no issues with the ModelForm or section_formset

class SiteVisitItemForm(forms.ModelForm):

    class Meta:
        model = models.SiteVisitItem
        exclude = "report", "project", "action_for", "action_complete", "number"

SiteVisitItemFormSet = forms.models.inlineformset_factory(
    models.SiteVisitReport, models.SiteVisitItem,
    form=SiteVisitItemForm,
    can_delete=True,
    extra=0,
    can_order=True,
)

class SiteVisitSectionForm(forms.Form):
    section_name = forms.CharField(max_length=128, required=False, widget=forms.TextInput(attrs={"placeholder": "Section heading"}))
    section_text = forms.CharField(max_length=1000, required=False, widget=forms.Textarea(attrs={"placeholder": "Introduction", "style": "height: 100px;"}))

SiteVisitSectionFormset = forms.formset_factory(
    form=SiteVisitSectionForm, can_delete=True, extra=0, can_order=True
)

Traceback (most recent call last):
  File "python3.10/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
  File "python3.10/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "python3.10/site-packages/django/views/generic/base.py", line 104, in view
    return self.dispatch(request, *args, **kwargs)
  File "python3.10/site-packages/fivestar_app/quality/views.py", line 129, in dispatch
    return super().dispatch(request, *args, **kwargs)
  File "python3.10/site-packages/django/contrib/auth/mixins.py", line 109, in dispatch
    return super().dispatch(request, *args, **kwargs)
  File "python3.10/site-packages/django/views/generic/base.py", line 143, in dispatch
    return handler(request, *args, **kwargs)
  File "python3.10/site-packages/fivestar_app/quality/views.py", line 222, in post
    if all([form.is_valid(), item_formset.is_valid(), section_formset.is_valid()]):
  File "python3.10/site-packages/django/forms/formsets.py", line 384, in is_valid
    self.errors
  File "python3.10/site-packages/django/forms/formsets.py", line 366, in errors
    self.full_clean()
  File python3.10/site-packages/django/forms/formsets.py", line 423, in full_clean
    for i, form in enumerate(self.forms):
  File "python3.10/site-packages/django/utils/functional.py", line 47, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "python3.10/site-packages/django/forms/formsets.py", line 205, in forms
    return [
  File "python3.10/site-packages/django/forms/formsets.py", line 206, in <listcomp>
    self._construct_form(i, **self.get_form_kwargs(i))
  File "python3.10/site-packages/django/forms/models.py", line 1120, in _construct_form
    form = super()._construct_form(i, **kwargs)
  File "python3.10/site-packages/django/forms/models.py", line 737, in _construct_form
    kwargs["initial"] = self.initial_extra[i - self.initial_form_count()]

Exception Type: KeyError at /quality/sitevisitreports/24022/2/items/
Exception Value: 0

the traceback appears to refer to this part of model form:

        elif self.initial_extra:
            # Set initial values for extra forms
            try:
                kwargs["initial"] = self.initial_extra[i - self.initial_form_count()]
            except IndexError:
                pass

given that self.initial_extra = initial and initial is a dictionary, is IndexError the right exception here?