django-filter messing around with empty field

I setup django-filter to filter some of my listings. Here is one of them, with a custom form:

class BookingListFiltersForm(forms.Form):

    state__in = forms.MultipleChoiceField(
        choices=Booking.STATE_CHOICES, required=False,
        label=_("État"), widget=forms.CheckboxSelectMultiple)
    source__in = forms.ModelMultipleChoiceField(
        queryset=Platform.objects.all(), required=False,
        label=_("Source"), widget=ModelSelect2Multiple(
            url='autocomplete:platform'))


class BookingManagerFilter(filters.FilterSet):

    payments__date = filters.DateFilter(method='payments__date_filter')
    payments__method = filters.ChoiceFilter(
        method='payments__method_filter',
        choices=BookingPayment.METHOD_CHOICES,
    )

    class Meta:
        model = Booking
        fields = {
            'period': [
                'endswith', 'endswith__gte', 'endswith__lte',
                'startswith', 'startswith__gte', 'startswith__lte',
            ],
            'state': ['in'],
            'source': ['in'],
            'booking_date': ['date', 'date__lte', 'date__gte'],
            'accommodation': ['in'],
            'guest': ['exact']
        }

    def get_form_class(self):
        return BookingListFiltersForm

    def payments__date_filter(self, queryset, name, value):
        return queryset.filter(**{name: value})

    def payments__method_filter(self, queryset, name, value):
        return queryset.filter(**{name: value})

The form is submitted by GET method. When the field "source__in" is empty, the querystring looks like this "?state__in=1". In such case, I have no result in my page (which is unexpected).

I looked at debug toolbar to have more information about the executed SQL query. Surprisingly, I found no SQL query for the related queryset! (while if querystring is "?state__in=1&source__in=2" for instance, the result is as expected, and I can find related queries in debug toolbar)

So I tried to force the impression of the SQL query using print(str(filters.qs.query)). New surprise, this triggered an EmptyResultSet exception:

Traceback:

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  35.             response = get_response(request)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  128.                 response = self.process_exception_by_middleware(e, request)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  126.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/views/generic/base.py" in view
  69.             return self.dispatch(request, *args, **kwargs)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/utils/decorators.py" in _wrapper
  62.             return bound_func(*args, **kwargs)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
  21.                 return view_func(request, *args, **kwargs)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/utils/decorators.py" in bound_func
  58.                 return func.__get__(self, type(self))(*args2, **kwargs2)

File "/home/tony/Workspace/cocoonr/utils/views/manager.py" in dispatch
  29.         return super().dispatch(*args, **kwargs)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/views/generic/base.py" in dispatch
  89.         return handler(request, *args, **kwargs)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/views/generic/list.py" in get
  142.         self.object_list = self.get_queryset()

File "/home/tony/Workspace/cocoonr/booking/views/manager.py" in get_queryset
  73.         queryset = super().get_queryset()

File "/home/tony/Workspace/cocoonr/utils/views/common.py" in get_queryset
  118.         print(self.filters.qs.query)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/db/models/sql/query.py" in __str__
  252.         sql, params = self.sql_with_params()

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/db/models/sql/query.py" in sql_with_params
  260.         return self.get_compiler(DEFAULT_DB_ALIAS).as_sql()

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/db/models/sql/compiler.py" in as_sql
  461.                 where, w_params = self.compile(self.where) if self.where is not None else ("", [])

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/db/models/sql/compiler.py" in compile
  393.             sql, params = node.as_sql(self, self.connection)

File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/django/db/models/sql/where.py" in as_sql
  98.                     raise EmptyResultSet

Exception Type: EmptyResultSet at /manager/booking/bookings/
Exception Value: 

Now I am stuck, I have no idea what is going wrong and how to debug any further.

I tried to pass the following querystring for the sake of testing: "?state__in=1&source__in=". In such case, the filtering works properly, but the filter form shows an error "« » is not a valid value" for the field "source__in".

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