Designate DNS – “List project limits” API returns “min_ttl”:null

[Arkady Shtempler]

“List project limits” API: https://docs.openstack.org/api-ref/dns/?expanded=get-the-name-servers-for-a-zone-detail,get-project-limits-detail,view-quotas-detail#get-project-limits
returns “min_ttl”:null instead some valid (integer) value.

{
  "max_page_limit": 1000,
  "max_recordset_name_length": 255,
  "max_recordset_records": 20,
  "max_zone_name_length": 255,
  "max_zone_records": 500,
  "max_zone_recordsets": 500,
  "max_zones": 10,
  "min_ttl": null
}

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/designate/+/918367