Exception when dataset is empty

[Suganya31]

Description

When a dataset is empty, the ConfidenceBasedFMeasureCalculator creates an exception.

GerbilException: java.lang.ArrayIndexOutOfBoundsException: 0 (error type -106: Got an unexpected exception while running the experiment.)
	at org.aksw.gerbil.execute.ExperimentTask.runExperiment(ExperimentTask.java:598)
	at org.aksw.gerbil.execute.ExperimentTask.run(ExperimentTask.java:167)
	at org.aksw.simba.topicmodeling.concurrent.workers.WorkerImpl.run(WorkerImpl.java:44)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
	at org.aksw.gerbil.evaluate.impl.ConfidenceBasedFMeasureCalculator.calculateOptMicroFMeasure(ConfidenceBasedFMeasureCalculator.java:104)
	at org.aksw.gerbil.evaluate.impl.ConfidenceBasedFMeasureCalculator.calculateMicroFMeasure(ConfidenceBasedFMeasureCalculator.java:75)
	at org.aksw.gerbil.evaluate.impl.ClassConsideringFMeasureCalculator.evaluate(ClassConsideringFMeasureCalculator.java:63)
	at org.aksw.gerbil.evaluate.AbstractTypeTransformingEvaluatorDecorator.evaluate(AbstractTypeTransformingEvaluatorDecorator.java:41)
	at org.aksw.gerbil.evaluate.AbstractTypeTransformingEvaluatorDecorator.evaluate(AbstractTypeTransformingEvaluatorDecorator.java:41)
	at org.aksw.gerbil.evaluate.SubTaskEvaluator.evaluate(SubTaskEvaluator.java:46)
	at org.aksw.gerbil.execute.ExperimentTask.evaluate(ExperimentTask.java:617)
	at org.aksw.gerbil.execute.ExperimentTask.runExperiment(ExperimentTask.java:592)
	... 5 more