Comment 4 for bug 1894966

yeah in 2.64 microversion request has been changed from 'policies' as array to single items as string
- https://review.opendev.org/#/c/567534/36/nova/api/openstack/compute/rest_api_version_history.rst

empty 'policies' was anyways wrong request which has been fixed in 2.64 by converting the array type to string field. What we can do is to improve the error code from 500 to 400 but do we need to improve the error code for older microversion? or should ask to use new microversion which already fixed the issue.