Attaching patch with null check and unit test exposing the issue.
Testing done: "mvn test"
To run the single test: "mvn -Dtest=TestGenericData#testValidateNullableEnum test"
Note that this is somewhat related to
AVRO-997. I see that the latest patch there includes this change:
+ if (!isEnum(datum)) return false;
I believe this change would probably address this issue as well. However, I think this particular change may not be backwards compatible. Currently you can pass in strings as I do in the unit test to validate and it works.