Django South: Changing a field from null = True to null = False

# We have this table
mysql> show columns from myapp_mymodel where Field = "my_field_id";

+-------------+---------+------+-----+---------+-------+
| Field       | Type    | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+-------+
| my_field_id | int(11) | YES  | MUL | NULL    |       |
+-------------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)


# We want to change this table so that column Null is NO for Field my_field_id


# First create an empty migration
bin/django schemamigration myapp mymodel_my_field_cannot_be_null --empty



#Then add the forward migration:
    def forwards(self, orm):
        #db.alter_column(table_name, column_name, field, explicit_name=True)
        db.alter_column('myapp_mymodel', 'my_field_id', models.ForeignKey(orm['myapp.MyModel'], null = False), explicit_name=True)


When this is run you get the following code executed:
DEBUG:django.db.backends:(0.000) SET FOREIGN_KEY_CHECKS=0;; args=()
DEBUG:south:south execute "
            SELECT kc.constraint_name, kc.column_name
            FROM information_schema.key_column_usage AS kc
            JOIN information_schema.table_constraints AS c ON
                kc.table_schema = c.table_schema AND
                kc.table_name = c.table_name AND
                kc.constraint_name = c.constraint_name
            WHERE
                kc.table_schema = %s AND
                kc.table_catalog IS NULL AND
                kc.table_name = %s AND
                c.constraint_type = %s
        " with params "['django', 'myapp_mymodel', 'FOREIGN KEY']"
DEBUG:django.db.backends:(0.111)
            SELECT kc.constraint_name, kc.column_name
            FROM information_schema.key_column_usage AS kc
            JOIN information_schema.table_constraints AS c ON
                kc.table_schema = c.table_schema AND
                kc.table_name = c.table_name AND
                kc.constraint_name = c.constraint_name
            WHERE
                kc.table_schema = django AND
                kc.table_catalog IS NULL AND
                kc.table_name = myapp_mymodel AND
                c.constraint_type = FOREIGN KEY
        ; args=['django', 'myapp_mymodel', 'FOREIGN KEY']
DEBUG:south:south execute "ALTER TABLE `myapp_mymodel` ;" with params "[]"
DEBUG:django.db.backends:(0.000) ALTER TABLE `myapp_mymodel` ;; args=[]
DEBUG:south:south execute "ALTER TABLE `myapp_mymodel` MODIFY `my_field_id` integer NOT NULL;;" with params "[]"
DEBUG:django.db.backends:(0.075) ALTER TABLE `myapp_mymodel` MODIFY `my_field_id` integer NOT NULL;;; args=[]
DEBUG:south:south execute "ALTER TABLE `myapp_mymodel` ALTER COLUMN `my_field_id` DROP DEFAULT;" with params "[]"
DEBUG:django.db.backends:(0.067) ALTER TABLE `myapp_mymodel` ALTER COLUMN `my_field_id` DROP DEFAULT;; args=[]
DEBUG:south:south execute "ALTER TABLE `myapp_mymodel` ADD CONSTRAINT `my_field_id_refs_id_15e652d5` FOREIGN KEY (`my_field_id`) REFERENCES `myapp_my_field` (`id`);" with params "[]"
DEBUG:django.db.backends:(0.283) ALTER TABLE `myapp_mymodel` ADD CONSTRAINT `my_field_id_refs_id_15e652d5` FOREIGN KEY (`my_field_id`) REFERENCES `myapp_my_field` (`id`);; args=[]
DEBUG:south:south execute "SET FOREIGN_KEY_CHECKS=1;" with params "[]"
DEBUG:django.db.backends:(0.000) SET FOREIGN_KEY_CHECKS=1;; args=[]
DEBUG:django.db.backends:(0.000) SELECT `south_migrationhistory`.`id`, `south_migrationhistory`.`app_name`, `south_migrationhistory`.`migration`, `south_migrationhistory`.`applied` FROM `south_migrationhistory` WHERE (`south_migrationhistory`.`app_name` = myapp  AND `south_migrationhistory`.`migration` = 0006_mymodel_my_field_cannot_be_null ); args=('myapp', '0006_mymodel_my_field_cannot_be_null')
DEBUG:django.db.backends:(0.000) INSERT INTO `south_migrationhistory` (`app_name`, `migration`, `applied`) VALUES (myapp, 0006_mymodel_my_field_cannot_be_null, 2011-09-16 14:37:50); args=('myapp', '0006_mymodel_my_field_cannot_be_null', u'2011-09-16 14:37:50')



# and the backward migraion is
    def backwards(self, orm):
        db.alter_column('myapp_mymodel', 'my_field_id', models.ForeignKey(orm['myapp.MyModel'], null = True), explicit_name=True)