I see a simliar error when trying to view current user or server sessions in a 3 node hazelcast cluster.
java.lang.NullPointerException
at com.jivesoftware.openfire.session.RemoteSession.doSynchronousClusterTask(Remote Session.java:175)
at com.jivesoftware.openfire.session.RemoteSession.isSecure(RemoteSession.java:132 )
at org.jivesoftware.openfire.admin.server_002dsession_002dsummary_jsp._jspService( server_002dsession_002dsummary_jsp.java:303)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:547)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.ja va:1359)
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:11 8)
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:52)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.ja va:1330)
at org.jivesoftware.util.LocaleFilter.doFilter(LocaleFilter.java:74)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.ja va:1330)
at org.jivesoftware.util.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingF ilter.java:50)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.ja va:1330)
at org.jivesoftware.admin.PluginFilter.doFilter(PluginFilter.java:78)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.ja va:1330)
at org.jivesoftware.admin.AuthCheckFilter.doFilter(AuthCheckFilter.java:164)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.ja va:1330)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:478)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:520)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:22 7)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:94 1)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:409)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:186 )
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:875 )
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandler Collection.java:250)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.jav a:149)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:110)
at org.eclipse.jetty.server.Server.handle(Server.java:349)
at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:441)
at org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConne ction.java:919)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:582)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:218)
at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:51 )
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.jav a:586)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java :44)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:598 )
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:533)
at java.lang.Thread.run(Thread.java:745)
However it only happens when im using encryption on the cluster. Furthermore the only encryption scheme that seems to work and keep the cluster in sync is the ssl encryption. I've disabled it for now and went to using stunnel to secure the communication.