"%r" needs to have a value for field "%s" before this many-to-many relationship can be used.

Raise code

lh_field, rh_field in self.source_field.related_fields:
                core_filter_key = '%s__%s' % (self.query_field_name, rh_field.name)
                self.core_filters[core_filter_key] = getattr(instance, rh_field.attname)
                self.pk_field_names[lh_field.name] = rh_field.name

            self.related_val = self.source_field.get_foreign_related_value(instance)
            if None in self.related_val:
                raise ValueError('"%r" needs to have a value for field "%s" before '
                                 'this many-to-many relationship can be used.' %
                                 (instance, self.pk_field_names[self.source_field_name]))
            # Even if this relation is not to pk, we require still pk value.
            # The wish is that the instance has been already saved to DB,
            # although having a pk value isn't a guarantee of that.
            if instance.pk is None:
                raise ValueError("%r instance needs to have a primary key value before "