SortedSetDocValues faceting throws NullPointerException from getTopChildren/getAllChildren for a dimension that is configured hierarchical but has no document in the reader, instead of returning null as the Facets javadoc says (regression since 9.3.0)
Finding LFV-527Area: facet / SortedSetDocValues faceting (AbstractSortedSetDocValueFacetCounts#prepareChildIteration, shared by SortedSetDocValuesFacetCounts and ConcurrentSortedSetDocValuesFacetCounts)Priority: mediumImpact: crashNovelty: 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 declare a facet dimension as hierarchical (FacetsConfig.setHierarchical("category", true)), index SortedSetDocValues facets in which no document has "category" yet, and call getTopChildren(10, "category") or getAllChildren("category") on SortedSetDocValuesFacetCounts or ConcurrentSortedSetDocValuesFacetCounts, expecting null, because the Facets javadoc says both methods return null 'if this dimension was never seen' and the same call for a flat dimension does. Instead both throw NullPointerException: Cannot read field "dimStartOrd" because "dimTree" is null (getTopChildren when the query has hits, always with the count-all constructor and the concurrent class; getAllChildren always). The cause is a shortcut added in 9.3.0 to AbstractSortedSetDocValueFacetCounts#prepareChildIteration, which reads dimTree.dimStartOrd for an empty path without checking that state.getDimTree(dim) is non-null, while the flat branch and the path branch next to it return null for the same case.
The test shows that SortedSetDocValuesFacetCounts#getAllChildren throws for a dimension that FacetsConfig declares hierarchical but no document in the reader has.
Expected vs actual
Expected null (Facets javadoc: "dimension was never seen"); actual NullPointerException: Cannot read field "dimStartOrd" because "dimTree" is null, 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/facet/build/libs/lucene-facet-$V.jar
CP=$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.facet.sortedset.TestSsdvHierarchicalDimNotIndexedThe module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.
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).
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.