ServerInfo does not check response from getThreadInfo for null

The ServerInfo MBean does not check the response from getThreadInfo for null. If getThreadInfo is called for a thread that no longer exists it returns null. Currently it is possible for the following NullPointerException to be logged: -

java.lang.NullPointerException
at sun.reflect.GeneratedMethodAccessor87.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.jboss.system.server.ServerInfo.getThreadCpuUtilization(ServerInfo.java:557)
at org.jboss.system.server.ServerInfo.listThreadCpuUtilization(ServerInfo.java:510)
at sun.reflect.GeneratedMethodAccessor113.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)