Concurrent modification in PCELOE algorithm

[md-k-sarker]

I am trying to run PCELOE (Parallel version of CELOE) algorithm but it gives java concurrent modification error.

A snippet of the log is:
Caused by: java.util.ConcurrentModificationException
at java.util.TreeMap$NavigableSubMap$SubMapIterator.prevEntry(TreeMap.java:1714)
at java.util.TreeMap$NavigableSubMap$DescendingSubMapKeyIterator.next(TreeMap.java:1818)
at org.dllearner.algorithms.celoe.PCELOE.getNextNodeToExpand(PCELOE.java:503)
at org.dllearner.algorithms.celoe.PCELOE.access$200(PCELOE.java:65)
at org.dllearner.algorithms.celoe.PCELOE$PCELOEWorker.run(PCELOE.java:1138)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)