"java.lang.Exception: Discovery component invocation failed" is thrown during the MBean Query in JBoss ON

Issue

• During the MBean Query in JBoss ON following Exception is fired:

2012-09-26 13:02:14,526 INFO  [ResourceDiscoveryComponent.invoker.daemon-4] (ems.impl.jmx.connection.DConnection)- Querying MBeanServer for all MBeans...
2012-09-26 13:02:14,624 WARN  [InventoryManager.discovery-1] (rhq.core.pc.inventory.InventoryManager)- Failure during discovery for [Cache] Resources - failed after 2 ms.
java.lang.Exception: Discovery component invocation failed.
        at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ComponentInvocationThread.call(DiscoveryComponentProxyFactory.java:297)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
        at org.rhq.plugins.jbosscache3.JBossCacheDetailDiscoveryComponent.discoverResources(JBossCacheDetailDiscoveryComponent.java:83)
        at sun.reflect.GeneratedMethodAccessor119.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ComponentInvocationThread.call(DiscoveryComponentProxyFactory.java:293)
        ... 5 more

This is probably due to some old servers in the cache that are no longer running.