NPE thrown by the ComputeProcessor due to a null SourceTable.table

[NassimBtk]

Problem:

C:\Program Files\MetricsHub>MetricsHubServiceManager.exe
Listening for transport dt_socket at address: 5005
Exception in thread "pool-85727-thread-2" java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because the return value of "org.sentrysoftware.metricshub.engine.strategy.source.SourceTable.getTable()" is null
        at org.sentrysoftware.metricshub.engine.strategy.source.compute.ComputeProcessor.process(ComputeProcessor.java:595)
        at org.sentrysoftware.metricshub.engine.connector.model.monitor.task.source.compute.DuplicateColumn.accept(DuplicateColumn.java:96)
        at org.sentrysoftware.metricshub.engine.strategy.source.compute.ComputeUpdaterProcessor.processCompute(ComputeUpdaterProcessor.java:201)
        at org.sentrysoftware.metricshub.engine.strategy.source.compute.ComputeUpdaterProcessor.process(ComputeUpdaterProcessor.java:106)
        at org.sentrysoftware.metricshub.engine.connector.model.monitor.task.source.compute.DuplicateColumn.accept(DuplicateColumn.java:96)
        at org.sentrysoftware.metricshub.engine.strategy.AbstractStrategy.processSourcesAndComputes(AbstractStrategy.java:203)
        at org.sentrysoftware.metricshub.engine.strategy.AbstractStrategy.processSourcesAndComputes(AbstractStrategy.java:99)
        at org.sentrysoftware.metricshub.engine.strategy.collect.CollectStrategy.processMonitorJob(CollectStrategy.java:243)
        at org.sentrysoftware.metricshub.engine.strategy.collect.CollectStrategy.lambda$collect$8(CollectStrategy.java:183)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.base/java.lang.Thread.run(Unknown Source)
        

This has been observed on other computes not only the DuplicateColumn.

Proposal:

Check the source processor that generates the null table otherwise it probably comes from a client library returning a null List<List<String>>.

Also, form the AbstractStrategy, skip the compute processing if sourcetable.table and sourcetable.rawRest are both null.