AVRO-3219: Add nullable enum type field support in Avro.Reflect

[RobertIndie]

Signed-off-by: Zike Yang zike@apache.org

Jira

• My PR addresses the following Avro Jira issues and references them in the PR title.
  • https://issues.apache.org/jira/browse/AVRO-3219

Tests

• My PR adds the following unit tests: TestNullableEnumResolution

Commits

• My commits all reference Jira issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• This is just a bug fix. No need doc.

[RyanSkraba]

Re: @blachniet @zcsizmadia @KyleSchoonover

This is marked for release 1.11.1 -- would it be possible to take some time to review?

[KalleOlaviNiemitalo]

I don't use Avro.Reflect myself, but I see how this change can improve support for nullable enums, and I don't think this can make anything worse.
The changes in LoadClassCache don't do anything about union schemas with nullable non-enum value types, or non-nullable enum types, but lang/csharp/src/apache/test/Reflect/TestFromAvroProject.cs has tests covering those and GitHub actions don't show any failure.

I approve this but recommend one optimization.

[KalleOlaviNiemitalo]

Please indicate in the PR title that this is specifically for Avro.Reflect.

[RyanSkraba]

Thanks for the review @KalleOlaviNiemitalo .

@RobertIndie If you can address the comments, we can probably get this into 1.11.1!

[RobertIndie]

If you can address the comments, we can probably get this into 1.11.1!

Great. I will do it today.

[RobertIndie]

Thanks for your review. PTAL again. @KalleOlaviNiemitalo @RyanSkraba

[KalleOlaviNiemitalo]

The C# code looks OK

[KalleOlaviNiemitalo]

GitHub actions show that tests passed. I think this is ready to be merged. @RyanSkraba

[RyanSkraba]

Thanks very much for the contribution @RobertIndie and the review @KalleOlaviNiemitalo