There is a bug in the Hazelcast plugin (OF 4.2.1) which causes a null pointer exception, when ClusterListener’s cleanupNode is called. The problem seems to happen if a hazelcast node in the cluster is getting shutdown / goes offline, but there are no sessions connected to it. The code makes the assumption that whatever nodeRoutes.get(…) returned is non-null, but that isn’t the case when there were no sessions associated with the node.
See ClusterListener.java, cleanupNode, Line 282 and Line 282.
Please create a JIRA if appropriate. I may have some free time to try and fix this one.