We have a test failure in multithreaded solving in OptaPlanner (please see the linked issue for details). Interestingly, it happens only with JDK11.

java.util.ConcurrentModificationException: null
at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1134)
at org.drools.core.impl.KnowledgeBaseImpl.getOrCreateExactTypeDeclaration(KnowledgeBaseImpl.java:1458)
at org.drools.core.common.NamedEntryPoint.update(NamedEntryPoint.java:324)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.update(StatefulKnowledgeSessionImpl.java:1570)
at org.optaplanner.core.impl.score.director.drools.DroolsScoreDirector.update(DroolsScoreDirector.java:254)