Hi I want to know what's wrong with my code, I am having a concurrentexception, and I assume this lines cause it, but i don't know which specific part. Thanks in advance 

The exception is shown below and the codes that the exception is pointing, I really dont know what causes the concurrent problem. thanks a lot for helping!

```
java.util.ConcurrentModificationException
    at java.util.HashMap$HashIterator.nextNode(HashMap.java:1437)
    at java.util.HashMap$KeyIterator.next(HashMap.java:1461)
    at org.wildfly.clustering.web.infinispan.session.InfinispanSessionManager.findListeners(InfinispanSessionManager.java:321)
    at org.wildfly.clustering.web.infinispan.session.InfinispanSessionManager.triggerPrePassivationEvents(InfinispanSessionManager.java:298)
    at org.wildfly.clustering.web.infinispan.session.InfinispanSessionManager$SchedulableSession.close(InfinispanSessionManager.java:375)
    at org.wildfly.clustering.web.undertow.session.DistributableSession.requestDone(DistributableSession.java:71)
    at io.undertow.servlet.spec.ServletContextImpl.updateSessionAccessTime(ServletContextImpl.java:730)
    at io.undertow.servlet.spec.HttpServletResponseImpl.responseDone(HttpServletResponseImpl.java:578)
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:308)
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:247)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:76)
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:166)
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:197)
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:759)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

```