keystonemiddleware invalid unknown uuid

[HYSong]

I found that there are too many "Invalid uuid" warnings in nova and cinder logs.

The full trace:
/var/lib/openstack/lib/python3.8/site-packages/pycadf/identifier.py:71: UserWarning: Invalid uuid: unknown. To ensure interoperability, identifiers should be a valid uuid.
  warnings.warn(('Invalid uuid: %s. To ensure interoperability, ')

service_info.uuid in initailize whith "unknown" in keystonemiddleware(https://opendev.org/openstack/keystonemiddleware/src/commit/2bda844bb219df355d74b5c5b21f86244921a1c2/keystonemiddleware/audit/_api.py#L250), but it isn't handled very well in some cases.