NPE at CacheManager restart and JMX

With enabled JMX, a CacheManager stop() and start() afterwards results into a NPE.

java.lang.NullPointerException
at org.infinispan.jmx.CacheManagerJmxRegistration.start(CacheManagerJmxRegistration.java:62)
at org.infinispan.manager.DefaultCacheManager.start(DefaultCacheManager.java:709)
at org.infinispan.jmx.ComponentsJmxRegistrationTest.testStopStartCM(ComponentsJmxRegistrationTest.java:75)