fix: Handled ctx=None for AvroDeserializer and ProtobufDeserializer

[and-ratajski]

Handled None value for optional parameter called ctx in both AvroDeserializer and ProtobufDeserializer.

closes #1939
closes #1973

---

The "optional" ctx parameter in __call__ method in AvroDeserializer and ProtobufDeserializer isn't optional at all... Despite method annotation that specifies type of this parameter as ctx: Optional[SerializationContext] = None is was required in the method logic and None value wasn't handled. This misbehavior (compered to previous releases) was already noticed in the issues mentioned above.

This PR contains fix that handles None value and hence gives backward compatibility.

Checklist

• Contains customer facing changes? Including API/behavior changes
• Did you add sufficient unit test and/or integration test coverage for this PR?

References

GH:

• Handling of null ctx in ProtobufDeserializer #1939
• Handling of null ctx in AvroDeserializer #1973

Open questions / Follow-ups

If this behavior is intended for some reason I would suggest:

• marking it as breaking change (e.g. version 3.0.0)
• changing type annotation for ctx parameter

[confluent-cla-assistant]

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[Copilot]

Pull Request Overview

This PR fixes the handling of a None value for the optional ctx parameter in both AvroDeserializer and ProtobufDeserializer, ensuring backward compatibility with previous releases.

• Updated the construction of the subject variable by adding a conditional check for None.
• Adjusted the dependency resolution to only execute when ctx is provided.
• Revised the CHANGELOG to document the fixes.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/confluent_kafka/schema_registry/protobuf.py	Updated subject resolution with a conditional check for None.
src/confluent_kafka/schema_registry/avro.py	Updated subject resolution and dependency resolution with a conditional check for None.
CHANGELOG.md	Documented the fixes regarding the ctx parameter.

[and-ratajski]

In addition, I tested in my application that uses AvroDeserializer - works

[rayokota]

/sem-approve

[rayokota]

Thanks @and-ratajski , LGTM