Swing text components often (but not always) throw NullPointerExceptions.

To reproduce, add Lucida Sans Regular to font.properties files
run Stylepad (java -jar Stylepad.jar) in /jdk1.4/demo/jfc/Stylepad directory,
select Hebrew Keymap or Arabic Keymap, select Lucida Sans from Font menu, then type some letters, very often, a list of exception occurred, see the attachment as belows.
The testing was using jdk1.4 Merlin release "b19" build, but might have been there since "F" build. This happens on both Solaris or Windows.

Exception occurred during event dispatching:
java.lang.NullPointerException
        at javax.swing.text.CompositeView.replace(CompositeView.java:197)
        at javax.swing.text.BoxView.replace(BoxView.java:149)
        at javax.swing.text.View.append(View.java:417)
        at javax.swing.text.FlowView$FlowStrategy.layoutRow(FlowView.java:492)
        at javax.swing.text.TextLayoutStrategy.layoutRow(TextLayoutStrategy.java:110)
        at javax.swing.text.FlowView$FlowStrategy.layout(FlowView.java:395)
        at javax.swing.text.TextLayoutStrategy.layout(TextLayoutStrategy.java:93)
        at javax.swing.text.FlowView.setSpan(FlowView.java:183)
        at javax.swing.text.BoxView.paint(BoxView.java:357)
        at javax.swing.text.ParagraphView.paint(ParagraphView.java:491)
        at javax.swing.text.AsyncBoxView$ChildLocator.paintChildren(AsyncBoxView.java:893)
        at javax.swing.text.AsyncBoxView.paint(AsyncBoxView.java:569)
        at javax.swing.text.ZoneView$Zone.paint(ZoneView.java:517)
        at javax.swing.text.BoxView.paintChild(BoxView.java:130)
        at javax.swing.text.BoxView.paint(BoxView.java:369)
        at javax.swing.plaf.basic.BasicTextUI$RootView.paint(BasicTextUI.java:1206)
        at javax.swing.plaf.basic.BasicTextUI.paintSafely(BasicTextUI.java:524)
        at javax.swing.plaf.basic.BasicTextUI.paint(BasicTextUI.java:658)
        at javax.swing.plaf.basic.BasicTextUI.update(BasicTextUI.java:637)
        at javax.swing.JComponent.paintComponent(JComponent.java:410)
        at javax.swing.JComponent.paint(JComponent.java:711)
        at javax.swing.JComponent.paintChildren(JComponent.java:516)
        at javax.swing.JComponent.paint(JComponent.java:720)
        at javax.swing.JViewport.paint(JViewport.java:681)
        at javax.swing.JComponent.paintWithBuffer(JComponent.java:4207)
        at javax.swing.JComponent._paintImmediately(JComponent.java:4150)
        at javax.swing.JComponent.paintImmediately(JComponent.java:3997)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:374)
        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:119)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:154)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:353)
        at java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:127)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:117)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:96)