UnifiedHighlighter with maxPassages=0 throws NullPointerException for every document that has a match (a per-field 0 makes the whole multi-field call fail)
Finding LFV-265Area: highlighter / UnifiedHighlighter passage selection (FieldHighlighter.maybeAddPassage; maxPassages is never range-checked by UnifiedHighlighter.highlightFieldsAsObjects)Priority: lowImpact: wrong errorNovelty: new
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
You call UnifiedHighlighter.highlight(field, query, topDocs, 0), or highlightFields with a per-field count of 0, and expect what the same call already does for a document without a match: a null snippet (or, if 0 is not allowed, an IllegalArgumentException that says so). Instead, for every document that has a match in the field, FieldHighlighter.maybeAddPassage tests passageQueue.size() == maxPassages (0 == 0) while the passage queue is still empty and then calls passageQueue.peek().getScore(), so a NullPointerException escapes the call. With {title: 0, body: 1} the body field, which asked for one passage, loses its snippet too, because the whole call throws.
The test shows that UnifiedHighlighter.highlight(field, query, topDocs, 0) fails with an internal NullPointerException for a document that matches in the field.
Expected vs actual
Expected a null snippet (or an up-front IllegalArgumentException); actual NullPointerException because PriorityQueue.peek() is null in FieldHighlighter.maybeAddPassage (FieldHighlighter.java:212), with -ea and -da.
Files
Run it
- Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
- Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
- Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
- 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=$CP:$LUCENE/lucene/highlighter/build/libs/lucene-highlighter-$V.jar
CP=$CP:$LUCENE/lucene/memory/build/libs/lucene-memory-$V.jar
CP=$CP:$LUCENE/lucene/queries/build/libs/lucene-queries-$V.jar
CP=$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" $(find src -name '*.java')
# run 1: assertions on, seed DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
-cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
execute --select-class org.apache.lucene.search.uhighlight.TestZeroMaxPassagesGradle 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).
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.