NullPointerException in MVCCLockManager of LOCK_CACHE in system repository of EPP 5.2

Issue

• Following warning appears periodically (20 minutes) in the server.log of our EPP 5.2.2 instance:

WARN  [org.jboss.cache.jmx.ResourceDMBean] Exception while reading value of attribute locks held
java.lang.reflect.InvocationTargetException
        at sun.reflect.GeneratedMethodAccessor600.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:616)
        at org.jboss.cache.jmx.ResourceDMBean$MethodAttributeEntry.invoke(ResourceDMBean.java:657)
        at org.jboss.cache.jmx.ResourceDMBean.getNamedAttribute(ResourceDMBean.java:537)
        at org.jboss.cache.jmx.ResourceDMBean.getAttribute(ResourceDMBean.java:185)
        at org.jboss.mx.server.RawDynamicInvoker.getAttribute(RawDynamicInvoker.java:117)
        at org.jboss.mx.server.MBeanServerImpl.getAttribute(MBeanServerImpl.java:565)
        at sun.reflect.GeneratedMethodAccessor584.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:616)
        at org.jboss.jmx.connector.invoker.InvokerAdaptorService.invoke(InvokerAdaptorService.java:266)
        at sun.reflect.GeneratedMethodAccessor313.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:616)
        at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:157)
        at org.jboss.mx.server.Invocation.dispatch(Invocation.java:96)
        at org.jboss.mx.interceptor.AbstractInterceptor.invoke(AbstractInterceptor.java:138)
        at org.jboss.mx.server.Invocation.invoke(Invocation.java:90)
        at org.jboss.mx.interceptor.ModelMBeanOperationInterceptor.invoke(ModelMBeanOperationInterceptor.java:140)
        at org.jboss.jmx.connector.invoker.SerializableInterceptor.invoke(SerializableInterceptor.java:74)
        at org.jboss.jmx.connector.invoker.AuthenticationInterceptor.invoke(AuthenticationInterceptor.java:107)
        at org.jboss.mx.server.Invocation.invoke(Invocation.java:90)
        at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
        at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:668)
        at org.jboss.invocation.jrmp.server.JRMPProxyFactory.invoke(JRMPProxyFactory.java:180)
        at sun.reflect.GeneratedMethodAccessor312.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:616)
        at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:157)
        at org.jboss.mx.server.Invocation.dispatch(Invocation.java:96)
        at org.jboss.mx.server.Invocation.invoke(Invocation.java:88)
        at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
        at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:668)
        at org.jboss.invocation.jrmp.server.JRMPInvoker$MBeanServerAction.invoke(JRMPInvoker.java:855)
        at org.jboss.invocation.jrmp.server.JRMPInvoker.invoke(JRMPInvoker.java:422)
        at sun.reflect.GeneratedMethodAccessor311.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:616)
        at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:322)
        at sun.rmi.transport.Transport$1.run(Transport.java:177)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
        at java.lang.Thread.run(Thread.java:679)
Caused by: java.lang.NullPointerException
        at org.jboss.cache.lock.MVCCLockManager.getNumberOfLocksHeld(MVCCLockManager.java:335)
        ... 49 more

Simultaneously, we see an ERROR in the agent.log of the JON agent.