Keystone role_assignments actions does not work

On current master version:
I found some of the Keystone Actions does not work.

keystone.role_assignments_create
keystone.role_assignments_delete
keystone.role_assignments_find
keystone.role_assignments_get
keystone.role_assignments_update

For example,
$ mistral run-action keystone.role_assignments_create
{"result": "Failed to run action [action_ex_id=None, action_cls='<class 'mistral.actions.action_factory.KeystoneAction'>', attributes='{u'client_method_name': u'role_assignments.create'}', params='{}']\n KeystoneAction.role_assignments.create failed: <class 'keystoneclient.exceptions.MethodNotImplemented'>: None"}

There was no implementation in the Keystone code.
https://github.com/openstack/python-keystoneclient/blob/master/keystoneclient/v3/role_assignments.py#L103
create
update
get
find
delete

At least, I think that we should be doing is following.
role_assignments_create: role_assignments.create -> roles.grant(openstack role add)
role_assignments_delete: role_assignments.delete -> roles.revoke(openstack role remove)

https://github.com/openstack/python-keystoneclient/blob/master/keystoneclient/v3/roles.py#L299
grant
revoke

Should I fix the next file when I want to solve this problem?
https://github.com/openstack/mistral/blob/master/mistral/actions/openstack/mapping.json