Merge ANTI JOIN should preserve unmatched NULL keys

[bvolpato]

Jira Link

Pending issue creation and linkage. This PR is a draft.

Changes Proposed

Enumerable merge ANTI joins currently stop processing left rows when they reach a NULL join key. Under strict equality, NULL keys do not match and those left rows must survive the ANTI join.

Preserve left NULL keys in all three merge-join advancement paths. Correct the existing ANTI test expectations and add repeated-NULL coverage. The tests also cover empty inputs, NULL keys on the right, and the overload with an additional predicate.

Reproduction

With ascending, NULLS LAST inputs, an equality ANTI join of left [1, 2, NULL] and right [1] returns [2]. The correct result is [2, NULL].

./gradlew :core:test --tests 'org.apache.calcite.runtime.EnumerablesTest'

Validation

• The updated test class fails in four methods against the baseline runtime.
• Compiling the changed runtime and running the complete EnumerablesTest class directly passes all 53 enabled tests; one existing test is disabled.
• Generated EnumerableMergeJoin execution returns [2, NULL] after the fix.
• ./gradlew autostyleApply and git diff --check pass.
• Focused runs used freshly compiled changed classes with cached supporting artifacts. Native Gradle test-class compilation on pristine main was blocked by java.io.IOException: No space left on device; the full Gradle build has not been validated locally.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud