Quoting Vladimir Sizikov (JavaTest Harness 4.5 ea b13 is used),

"Once I created the configuration, and then closed the test suite and opened the workdir again, I see multiple exceptions

Exception in thread "ContextMgr Refresh Defer" java.lang.NullPointerException
        at com.sun.javatest.exec.TestTreePanel$PanelModel.refreshTree(TestTreePanel.java:1966)
        at com.sun.javatest.exec.ExecTool.unpauseTreeCacheWork(ExecTool.java:611)
        at com.sun.javatest.exec.ContextManager.refreshTestsImpl(ContextManager.java:319)
        at com.sun.javatest.exec.ContextManager.access$000(ContextManager.java:75)
        at com.sun.javatest.exec.ContextManager$1.run(ContextManager.java:242)
        at java.lang.Thread.run(Thread.java:662)
"

We either need this fixed or explained what should be done to prevent these exceptions to be thrown.
Please close the issue if this is a duplicate.