Harness throws NPE on attempt to init Tests Tree GUI when user has already closed test suite

Javatest 4.2_b08, b09 (Dec 29)

- Start the tool
- Open Testsuite or Working Directory that has a big number of tests so it takes some time to load them (i.e. JDTS testsuite)
- Once Harness painted Tests tree in its initial state (showing "tests-are-being-read" progress marks) - do a File/Close.
- Wait a few seconds (I guess until background thread finishes reading tests). Watch for console output:

Exception in thread "Test tree updater" java.lang.NullPointerException
at com.sun.javatest.exec.TestTreePanel$6$1.run(TestTreePanel.java:867)
Most recent stack trace is:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javax.swing.tree.TreePath.hashCode(TreePath.java:213)
        at java.util.Hashtable.get(Hashtable.java:336)
        at javax.swing.tree.FixedHeightLayoutCache.getMapping(FixedHeightLayoutCache.java:578)
        at javax.swing.tree.FixedHeightLayoutCache.getNodeForPath(FixedHeightLayoutCache.java:671)
        at javax.swing.tree.FixedHeightLayoutCache.treeNodesChanged(FixedHeightLayoutCache.java:331)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.treeNodesChanged(BasicTreeUI.java:3671)
        at com.sun.javatest.exec.TestTreeModel$Notifier.run(TestTreeModel.java:1480)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)


Line 1480 is this loop:
                   for (int i = 0; i < l.length; i++) {
                        ((TreeModelListener) l[i]).treeNodesChanged(e);
                    }
                    break;