Enable org.opensearch.knn.integ.DerivedSourceIT tests that were ignored before

[reta]

Description

Enable org.opensearch.knn.integ.DerivedSourceIT tests that were ignored before

Related Issues

Followup on #264

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[reta]

Observed failures:

» [2026-03-20T08:28:57,283][WARN ][r.suppressed             ] [integTest-0] path: derivedit-original-enable-testnestedfieldkmdtvs/_doc/1, params: {index=derivedit-original-enable-testnestedfieldkmdtvs, id=1}
»  org.opensearch.transport.RemoteTransportException: [integTest-0][127.0.0.1:62505][indices:data/read/get[s]]
»  Caused by: java.lang.NullPointerException: Cannot read the array length because "vector" is null
»       at org.opensearch.knn.index.vectorvalues.KNNFloatVectorValues.getVector(KNNFloatVectorValues.java:28)
»       at org.opensearch.knn.index.vectorvalues.KNNFloatVectorValues.getVector(KNNFloatVectorValues.java:20)
»       at org.opensearch.knn.index.codec.derivedsource.AbstractPerFieldDerivedVectorTransformer.formatVector(AbstractPerFieldDerivedVectorTransformer.java:32)
»       at org.opensearch.knn.index.codec.derivedsource.NestedPerFieldDerivedVectorTransformer.apply(NestedPerFieldDerivedVectorTransformer.java:41)
»       at org.opensearch.common.xcontent.support.XContentMapValues.processEntry(XContentMapValues.java:770)
»       at org.opensearch.common.xcontent.support.XContentMapValues.processMap(XContentMapValues.java:748)
»       at org.opensearch.common.xcontent.support.XContentMapValues.processStack(XContentMapValues.java:737)
»       at org.opensearch.common.xcontent.support.XContentMapValues.lambda$transform$0(XContentMapValues.java:715)
»       at org.opensearch.knn.index.codec.derivedsource.DerivedSourceVectorTransformer.injectVectors(DerivedSourceVectorTransformer.java:163)
»       at org.opensearch.knn.index.codec.derivedsource.DerivedSourceStoredFieldVisitor.binaryField(DerivedSourceStoredFieldVisitor.java:29)
»       at org.apache.lucene.index.StoredFieldVisitor.binaryField(StoredFieldVisitor.java:54)
»       at org.apache.lucene.codecs.lucene90.compressing.Lucene90CompressingStoredFieldsReader.readField(Lucene90CompressingStoredFieldsReader.java:267)
»       at org.apache.lucene.codecs.lucene90.compressing.Lucene90CompressingStoredFieldsReader.document(Lucene90CompressingStoredFieldsReader.java:681)
»       at org.opensearch.knn.index.codec.KNN10010Codec.KNN10010DerivedSourceStoredFieldsReader.document(KNN10010DerivedSourceStoredFieldsReader.java:73)
»       at org.apache.lucene.index.CodecReader$1.document(CodecReader.java:101)
»       at org.opensearch.index.get.ShardGetService.innerGetLoadFromStoredFields(ShardGetService.java:281)
»       at org.opensearch.index.get.ShardGetService.innerGet(ShardGetService.java:240)
»       at org.opensearch.index.get.ShardGetService.get(ShardGetService.java:142)
»       at org.opensearch.index.get.ShardGetService.get(ShardGetService.java:126)
»       at org.opensearch.action.get.TransportGetAction.shardOperation(TransportGetAction.java:156)
»       at org.opensearch.action.get.TransportGetAction.shardOperation(TransportGetAction.java:62)
»       at org.opensearch.action.support.single.shard.TransportSingleShardAction.lambda$asyncShardOperation$0(TransportSingleShardAction.java:135)
»       at org.opensearch.action.ActionRunnable.lambda$supply$0(ActionRunnable.java:74)
»       at org.opensearch.action.ActionRunnable$2.doRun(ActionRunnable.java:89)
»       at org.opensearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:977)
»       at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52)
»       at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
»       at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
»       at java.base/java.lang.Thread.run(Thread.java:1474)

Reproducer: ./gradlew ':integTest' --tests 'org.opensearch.knn.integ.DerivedSourceIT.testNestedField' -Dtests.seed=60650EDDFF9ACC4B