Vague error message when building startree schema if there is a typo in the aggregate columns

The NullPointerException does not say what field has the typo.

java.lang.RuntimeException: Caught exception during running - org.apache.pinot.plugin.ingestion.batch.standalone.SegmentGenerationJobRunner
at org.apache.pinot.spi.ingestion.batch.IngestionJobLauncher.kickoffIngestionJob(IngestionJobLauncher.java:121) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.spi.ingestion.batch.IngestionJobLauncher.runIngestionJob(IngestionJobLauncher.java:94) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.tools.admin.command.LaunchDataIngestionJobCommand.execute(LaunchDataIngestionJobCommand.java:123) [pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.tools.admin.PinotAdministrator.execute(PinotAdministrator.java:156) [pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.tools.admin.PinotAdministrator.main(PinotAdministrator.java:168) [pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
Caused by: java.lang.NullPointerException
at org.apache.pinot.core.startree.v2.builder.BaseSingleTreeBuilder.(BaseSingleTreeBuilder.java:153) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.startree.v2.builder.OffHeapSingleTreeBuilder.(OffHeapSingleTreeBuilder.java:69) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.startree.v2.builder.MultipleTreesBuilder.getSingleTreeBuilder(MultipleTreesBuilder.java:140) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.startree.v2.builder.MultipleTreesBuilder.build(MultipleTreesBuilder.java:118) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.segment.creator.impl.SegmentIndexCreationDriverImpl.buildStarTreeV2IfNecessary(SegmentIndexCreationDriverImpl.java:277) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.segment.creator.impl.SegmentIndexCreationDriverImpl.handlePostCreation(SegmentIndexCreationDriverImpl.java:239) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.segment.creator.impl.SegmentIndexCreationDriverImpl.build(SegmentIndexCreationDriverImpl.java:199) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.plugin.ingestion.batch.common.SegmentGenerationTaskRunner.run(SegmentGenerationTaskRunner.java:102) ~[pinot-batch-ingestion-standalone-0.4.0-SNAPSHOT-shaded.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.plugin.ingestion.batch.standalone.SegmentGenerationJobRunner.run(SegmentGenerationJobRunner.java:190) ~[pinot-batch-ingestion-standalone-0.4.0-SNAPSHOT-shaded.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.spi.ingestion.batch.IngestionJobLauncher.kickoffIngestionJob(IngestionJobLauncher.java:119) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
... 4 more
Exception caught:
java.lang.RuntimeException: Caught exception during running - org.apache.pinot.plugin.ingestion.batch.standalone.SegmentGenerationJobRunner
at org.apache.pinot.spi.ingestion.batch.IngestionJobLauncher.kickoffIngestionJob(IngestionJobLauncher.java:121) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.spi.ingestion.batch.IngestionJobLauncher.runIngestionJob(IngestionJobLauncher.java:94) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.tools.admin.command.LaunchDataIngestionJobCommand.execute(LaunchDataIngestionJobCommand.java:123) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.tools.admin.PinotAdministrator.execute(PinotAdministrator.java:156) [pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.tools.admin.PinotAdministrator.main(PinotAdministrator.java:168) [pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
Caused by: java.lang.NullPointerException
at org.apache.pinot.core.startree.v2.builder.BaseSingleTreeBuilder.(BaseSingleTreeBuilder.java:153) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.startree.v2.builder.OffHeapSingleTreeBuilder.(OffHeapSingleTreeBuilder.java:69) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.startree.v2.builder.MultipleTreesBuilder.getSingleTreeBuilder(MultipleTreesBuilder.java:140) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.startree.v2.builder.MultipleTreesBuilder.build(MultipleTreesBuilder.java:118) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.segment.creator.impl.SegmentIndexCreationDriverImpl.buildStarTreeV2IfNecessary(SegmentIndexCreationDriverImpl.java:277) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.segment.creator.impl.SegmentIndexCreationDriverImpl.handlePostCreation(SegmentIndexCreationDriverImpl.java:239) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.core.segment.creator.impl.SegmentIndexCreationDriverImpl.build(SegmentIndexCreationDriverImpl.java:199) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.plugin.ingestion.batch.common.SegmentGenerationTaskRunner.run(SegmentGenerationTaskRunner.java:102) ~[pinot-batch-ingestion-standalone-0.4.0-SNAPSHOT-shaded.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.plugin.ingestion.batch.standalone.SegmentGenerationJobRunner.run(SegmentGenerationJobRunner.java:190) ~[pinot-batch-ingestion-standalone-0.4.0-SNAPSHOT-shaded.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
at org.apache.pinot.spi.ingestion.batch.IngestionJobLauncher.kickoffIngestionJob(IngestionJobLauncher.java:119) ~[pinot-all-0.4.0-SNAPSHOT-jar-with-dependencies.jar:0.4.0-SNAPSHOT-b40dd992874f9bc38b911870e041a8f6e24c3776]
... 4 more

Start at org.apache.pinot.core.startree.v2.builder.BaseSingleTreeBuilder, where the NullPointerException is reported at line 153, and trace the callers through MultipleTreesBuilder and SegmentIndexCreationDriverImpl. Done means a typo in an aggregate column produces an error that identifies the offending field instead of only reporting a NullPointerException.

Written by the indexing model from the issue text.