class DocumentFilterSet(FilterSet):
    period = django_filters.ChoiceFilter(
        choices=Periods.choices,
        label='Period',
        field_name='period',
        method='period_filter',
    )
    
    def period_filter(self, queryset, name, value):
        if value:
            return queryset.filter(period=value)
        else:
            return queryset.filter(period='default_period')