Bug 67890 [PropertiesView] Exception when entries added to properties view
bundles/org.eclipse.ui.views/src/org/eclipse/ui/views/properties/PropertySheetViewer.java
}
    /**
     * The expand icon for a node in this viewer has been selected to collapse a
     * subtree. Deactivate the cell editor
     * 
     * @param event
     *            the SWT tree event
     */
    private void handleTreeCollapse(TreeEvent event) {
        if (cellEditor != null) {
            applyEditorValue();
            deactivateCellEditor();
        }
    }
    /**
     * The expand icon for a node in this viewer has been selected to expand the
     * subtree. Create the children 1 level deep.
     * <p>
     * Note that we use a "dummy" item (no user data) to show a "+" icon beside
     * an item which has children before the item is expanded now that it is
     * being expanded we have to create the real child items
     * </p>
     * 
     * @param event
     *            the SWT tree event
     */
    private void handleTreeExpand(TreeEvent event) {
        createChildren(event.item);
    }
    /**