Unrecognized field: schemaType (HTTP status code 422, SR code 422)

[ffissore]

Description

We run schema registry 5.1.4 (confluentinc/cp-schema-registry:5.1.4), which returns 422 when registering schemas using the latest confluent-kafka version, 2.6.2.
The culprit is PR #1852, specifically these lines: they are hard to catch because they buried under 12000 changed lines

How to reproduce

Run cp-{kafka,zookeeper,schema-registry}-5.1.4 and try registering a schema.

Checklist

Please provide the following information:

• confluent-kafka-python and librdkafka version (confluent_kafka.version() and confluent_kafka.libversion()): ('2.6.2', 33948160), ('2.6.1', 33948159)
• Apache Kafka broker version: 2.1.1 (cp-kafka:5.1.4)
• Client configuration: {...}: unrelated
• Operating system: unrelated
• Provide client logs (with 'debug': '..' as necessary): schema registry client doesn't log, however, this is the body of the request sent by it {"schema": "{\\"type\\": \\"record\\", \\"name\\": \\"HelloWorldValue\\", \\"fields\\": [{\\"type\\": \\"string\\", \\"name\\": \\"hello\\"}]}", "schemaType": "AVRO", "references": []}
• Provide broker log excerpts: unrelated
• Critical issue: no but it prevents us from upgrading the library

[rayokota]

@ffissore , are you able to upgrade to CP 5.5+?

[ffissore]

I'm not. We know we are lagging behind but the migration/upgrade has always been postponed and I have no idea when it will be prioritised.