AVRO-4238: [java] Fix Schema Evolution of Unions with an Array Default Value#3730
Merged
RyanSkraba merged 1 commit intoapache:mainfrom May 7, 2026
Conversation
When FastReader was enabled and a field of type Union<Array, ...> with an Array as default value was added, an AvroRuntimeException occurred during Schema Evolution. This change resolves this bug in FastReaderBuilder.java, allowing the Schema Migration to succeed as specified.
cedricholzer
force-pushed
the
avro-4238-fix-union-with-empty-array-default
branch
from
78bc7da to
9f70011
Compare
RyanSkraba
changed the title
RyanSkraba
approved these changes
May 7, 2026
Contributor
RyanSkraba
left a comment
RyanSkraba
left a comment
There was a problem hiding this comment.
OK, this LGTM -- it's a good catch, and the parallel problem shouldn't occur in Map (for example) because you don't need the schema to create a new, empty map. Thanks for the contribution!
RyanSkraba
pushed a commit
that referenced
this pull request
May 7, 2026
…3730) When FastReader was enabled and a field of type Union<Array, ...> with an Array as default value was added, an AvroRuntimeException occurred during Schema Evolution. This change resolves this bug in FastReaderBuilder.java, allowing the Schema Migration to succeed as specified.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
What is the purpose of the change
When FastReader is enabled and a field of type
union<array<?>>with an array as default value is added, the Schema Evolution fails and throws an AvroRuntimeException (for more details see AVRO-4238).This change fixes the root cause of the bug in
FastReaderBuilder.java. If the field schema is of typeUnion, then the first nestedArraytype is unboxed and passed toGenericData::newArray(which expects anArrayschema) instead of theUnionschema.While touching
TestReadingWritingDataInEvolvedSchemas.java, this PR also removes unused imports and consistently usesorg.junit.jupiter.api.Assertionslike the rest of the project instead of mixing it withorg.junit.Assert.Verifying this change
This change added tests and can be verified as follows:
union<array<>> = []. This test reproduces the bug on main, throwing an AvroRuntimeException, but passes on the fixed branch.Documentation
This PR does not introduce new features. No documentation was added or edited.