Fix filterset to be unbound when no GET parameters are passed

[marciomazza]

Fix the filterset to be unbound on a request with no get parameters.

This is necessary to set the filterset's (and it's form) initial values.

See
https://github.com/carltongibson/django-filter/blob/635343ec55c9928bfa297314711df77fa83ff6c7/django_filters/filterset.py#L198

[carltongibson]

Hi @marciomazza — thanks for the PR.

... necessary to set the filterset's (and it's form) initial values.

Can you explain your use-case in more detail please? I have a suspicion this isn't the change you're looking for, but I'd like to hear your side of it fully first. Thanks.

[marciomazza]

Oh... never mind.

I was trying set an initial value on a Filterset's field doing the following. Now I realize it doesn't work, even with this PR:

class EventFilter(django_filters.FilterSet):
    date = django_filters.DateFilter(
        field_name="event_date",
        widget=forms.DateInput(attrs={"type": "date"}),
        initial=date.today,
    )

    class Meta:
        model = Event
        fields = ["date"]

This, though, works (without the PR):

class EventFilter(django_filters.FilterSet):
    date = django_filters.DateFilter(
        field_name="event_date",
        widget=forms.DateInput(attrs={"type": "date"}),
    )

    class Meta:
        model = Event
        fields = ["date"]

    def __init__(self, data=None, *args, **kwargs):
        if not data:
            data = {"date": date.today()}
        super().__init__(data, *args, **kwargs)