Fixed #21917: Overly cautious SQLite3 backend for null fields + defaults

        # Special-case implicit M2M tables

        if isinstance(field, ManyToManyField) and field.rel.through._meta.auto_created:

            return self.create_model(field.rel.through)

        # Detect bad field combinations

        if (not field.null and

           (not field.has_default() or field.get_default() is None) and

           not field.empty_strings_allowed):

            raise ValueError("You cannot add a null=False column without a default value on SQLite.")

        self._remake_table(model, create_fields=[field])

    def remove_field(self, model, field):