Ccompat compatibility check returns 40402 for unknown latest schema

[GFriedrich]

Description

Registry Version: 3.0.6
Persistence type: in-memory

When checking the compatibility for a new/unknown schema on the latest version, the API returns a 40402 error for an "unknown" version. But actually the Confluent registry returns a successful compatibility check, as the check for an unknown latest schema is explicitly excluded:
https://github.com/confluentinc/schema-registry/blob/99303198f5776bf1f44947dcceea8a9f582655eb/core/src/main/java/io/confluent/kafka/schemaregistry/rest/resources/CompatibilityResource.java#L144

Environment

Local docker setup

Steps to Reproduce

1. Create a fresh Apicurio installation
2. Call the compatibility check for an unknown latest schema (e.g. at /compatibility/subjects/something/versions/latest)
3. See that the result is different.

Expected vs Actual Behaviour

The compatibility check for an unknown latest schema should just succeed. But currently it fails with a 40402 error.

[EricWittmann]

This has been fixed. I mean, this is really weird behavior on the part of the Confluent Schema Registry. But there's no doubt you're right about how it works and that the behavior is intentional. 🤯

Thanks for the report.

[GFriedrich]

Yea, not saying that this is a great behavior. Unfortunately I found though that certain integrations rely on this. 😒
So thanks for aligning this. Much appreciated. 🙏

[EricWittmann]

Sure thing. We do want the behavior to be as close as possible, for obvious interoperability reasons. So if you find other issues like this for sure let us know! 👍