In https://folio-org.atlassian.net/browse/RMB-346#icft=RMB-346 and https://folio-org.atlassian.net/browse/RMB-347#icft=RMB-347 we removed the database trigger that inserts a random UUID into the id field if the id field is empty. The client, not the database server, needs to create the UUID to prevent different database nodes (pg-pool replication environment) from having different UUIDs for the same record.

PgUtil.post already creates the random UUID.
For PostgresClient.save this feature needs to be added.
This is a new feature, not a regression, because "populateJsonWithId: true" was required in schema.json to enable the database trigger that creates the UUID.