Description of problem:
Web application context metrics are not being collected and result in an NPE. This is a regression from JBoss ON 3.1.0. The metrics that seem to be affected are:

rejectedSessions, sessionMaxAliveTime, sessionCounter, expiredSessions, maxActive, sessionAverageAliveTime, activeSessions

Version-Release number of selected component (if applicable):
4.4.0.JON311GA

How reproducible:
Always

Steps to Reproduce:
1.  Install and start EAP 5.1.2 server using all profile
2.  Start JBoss ON system
3.  Import EAP server into inventory
4.  Navigate to the *Monitoring* page of the //localhost/jxm-console web application context:

        <platform> / JBossAS Servers / EAP <host:port> all / Applications / Web Application (WAR)s / jmx-console.war / Web Application Contexts / //localhost/jmx-console > Monitoring 

5.  Enable the metric *Currently Active Sessions* and set its collection interval to 1 minute

It may take several minutes for the new value to take affect. It may simply be quicker to restart the agent at this point so that you can be certain that the new collection schedule will take affect.
  
Actual results:
No metrics appear in JBoss ON UI and agent logs the following error each time metric collection is attempted:

ERROR [ResourceContainer.invoker.daemon-5] (org.rhq.plugins.jbossas5.WebApplicationContextComponent)- Failed to collect metric 'activeSessions' for {JBossAS5}Web Application Context Resource with key localhost.
java.lang.NullPointerException
	at org.rhq.plugins.jbossas5.WebApplicationContextComponent.getValues(WebApplicationContextComponent.java:146)
	at sun.reflect.GeneratedMethodAccessor85.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:616)
	at org.rhq.core.pc.inventory.ResourceContainer$ComponentInvocationThread.call(ResourceContainer.java:634)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
	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:636)


Expected results:
Metrics should be collected normally and UI should reflect metrics.

Additional info:
This is a direct result of commit http://git.fedorahosted.org/cgit/rhq/rhq.git/commit/?id=88c286048d73a963eb2e2debd1009d8ed0d595b0 from bug 837510 is what breaks this. Prior to this commit, the variable clustered was initialized. However, this commit changed the type to an object without being initialized resulting in <null> being the default value whereas the existing code does not expect this. It appears that the initialization and retrieval of the web application context's clustered property was re-factored resulting in a non-initialized variable being used when attempting to retrieve the mentioned metrics.