def __init__(self, field, request, params, model, model_admin, field_path):
self.lookup_choices = flatten_choices(self.field_choices(field, request, model_admin))
self.lookup_kwarg_isnull = '{0}__isnull'.format(field_path)
self.lookup_val_isnull = request.GET.get(self.lookup_kwarg_isnull)
super(LazyChoicesFieldListFilter, self).__init__(field, request, params, model, model_admin, field_path)
self.empty_value_display = get_empty_value_display(model_admin)
