The NPE above has been seen several times while running some several hours long tests.
That means it is not so easy to reproduce but it surely occurs let's say once a week according tests run every day.

....java.lang.NullPointerException
    at com.sun.corba.se.impl.protocol.SharedCDRClientRequestDispatcherImpl.marshalingComplete(SharedCDRClientRequestDispatcherImpl.java:178)
    at com.sun.corba.se.impl.protocol.CorbaClientDelegateImpl.invoke(CorbaClientDelegateImpl.java:129)
    at org.omg.CORBA.portable.ObjectImpl._invoke(ObjectImpl.java:457)
    at com.sun.jmx.remote.internal.ProxyStub._invoke(Unknown Source)
    at org.omg.stub.javax.management.remote.rmi._RMIConnection_Stub.getConnectionId(Unknown Source)
    at javax.management.remote.rmi.RMIConnector.getConnectionId(RMIConnector.java:338)
    at javax.management.remote.rmi.RMIConnector.connect(RMIConnector.java:300)
    at javax.management.remote.rmi.RMIConnector.connect(RMIConnector.java:227)
    at javasoft.sqe.jmx.test.perf_footprint.MemoryLeakTest.doAction(MemoryLeakTest.java:248)
    at javasoft.sqe.jmx.test.perf_footprint.MemoryLeakTest.run(MemoryLeakTest.java:150)
    at javasoft.sqe.jmx.share.TestStarter.<init>(TestStarter.java:40)
    at javasoft.sqe.jmx.share.TestStarter.main(TestStarter.java:98)