The term-vectors reader of the merged view that IndexWriter hands to OneMerge#reorder (SlowCompositeCodecReaderWrapper) throws NullPointerException from clone() as soon as one merged segment has no term vectors, although the same class handles that null sub-reader in get, prefetch, checkIntegrity and close; on the merge path this closes the IndexWriter (since 9.9.0)

Finding LFV-1218Area: core / index: SlowCompositeCodecReaderWrapper (merged CodecReader view handed to OneMerge#reorder), term vectorsPriority: lowImpact: minorNovelty: new

Finding page for LFV-1218

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You write a merge policy whose OneMerge#reorder clones the term-vectors reader of the merged view it receives, and merge (or addIndexes) a segment with term vectors together with one in which no document has a term-vector field, expecting a reader that returns the first segment's term vectors, as the uncloned reader does. Instead clone() throws NullPointerException at SlowCompositeCodecReaderWrapper.java:233: the view stores a null sub-reader for the segment without term vectors (:206-213), and clone() maps TermVectorsReader::clone over that array (:230-235) without the null check that get, prefetch and checkIntegrity have and that close gets from IOUtils.close. On the merge path the exception closes the IndexWriter as a tragic event, and it fails the same way after a reopen.

Expected vs actual

Expected: clone() returns a reader whose get(0) returns doc 0's term vectors.
Actual: NullPointerException at SlowCompositeCodecReaderWrapper$SlowCompositeTermVectorsReaderWrapper.clone(SlowCompositeCodecReaderWrapper.java:233), thrown out of addIndexes.

Files

src/org/apache/lucene/index/TestMergedViewTermVectorsClone.java (JUnit test)

Run it

Tested on Lucene main 5adff78bb168 (2026-11-02): reproduced.
How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes -cp "$CP" $(find src -name '*.java')

# run 1: assertions off (production-like), seed DEADBEEF
java -da -dsa -Dtests.asserts=false -Xmx1g --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.index.TestMergedViewTermVectorsClone

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Files shown on the finding page

TestMergedViewTermVectorsClone.java

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.