Action sur un combobox et Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

salut

Bon moi j ai un gros probleme et j ai vraiment besoin de votre aide
donc j ai deux combobox dans la premiere j ai des services et dans la deuxieme j ai les debits utilisés pour ces services
il faut que quand je fixe le service "voice" dans le 1er combobox le 2eme combobox affiche seulement le débit "12.2" et devient disabled . Pour ça j ai écris un code qui a fonctionné:

private void jComboBox1ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        int modifiers;
         if (evt instanceof ActionEvent) {
              modifiers = ((ActionEvent)evt).getModifiers();
              long modsLong = modifiers & ActionEvent.MOUSE_EVENT_MASK;
              if (modsLong == MouseEvent.BUTTON1_MASK) {
               //   System.out.println(this.jComboBox1.getItemAt(this.jComboBox1.getSelectedIndex()).toString());
                  if(this.jComboBox1.getItemAt(this.jComboBox1.getSelectedIndex()).toString().equalsIgnoreCase("voice")){
                  this.jComboBox2.removeAllItems();
                  this.jComboBox2.addItem("12.2");
                  this.jComboBox2.setEnabled(false);
                  }else
                      GetServicesRate();
                 
              }
         }

mais seulement au début maintenant quand je sélectionne voice dans le combobox1 il n'affiche plus rien dans le combobox2 et l affichage devient bizare et quand j essaye de selectionner un autre service l affichage ne change pas et le combobox2 reste aussi vide.

et l'exception suivante apparait:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:991)
        at java.lang.Double.parseDouble(Double.java:510)
        at BudgetLink_View.TestingForm.jComboBox2ActionPerformed(TestingForm.java:648)
        at BudgetLink_View.TestingForm.access$100(TestingForm.java:22)
        at BudgetLink_View.TestingForm$2.actionPerformed(TestingForm.java:143)
        at javax.swing.JComboBox.fireActionEvent(JComboBox.java:1242)
        at javax.swing.JComboBox.contentsChanged(JComboBox.java:1313)
        at javax.swing.JComboBox.intervalRemoved(JComboBox.java:1333)
        at javax.swing.AbstractListModel.fireIntervalRemoved(AbstractListModel.java:161)
        at javax.swing.DefaultComboBoxModel.removeAllElements(DefaultComboBoxModel.java:169)
        at javax.swing.JComboBox.removeAllItems(JComboBox.java:753)
        at BudgetLink_View.TestingForm.GetServicesRate(TestingForm.java:710)
        at BudgetLink_View.TestingForm.jComboBox1ActionPerformed(TestingForm.java:607)
        at BudgetLink_View.TestingForm.access$000(TestingForm.java:22)
        at BudgetLink_View.TestingForm$1.actionPerformed(TestingForm.java:134)
        at javax.swing.JComboBox.fireActionEvent(JComboBox.java:1242)
        at javax.swing.JComboBox.setSelectedItem(JComboBox.java:569)
        at javax.swing.JComboBox.setSelectedIndex(JComboBox.java:605)
        at javax.swing.plaf.basic.BasicComboPopup$Handler.mouseReleased(BasicComboPopup.java:814)
        at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:273)
        at java.awt.Component.processMouseEvent(Component.java:6038)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3260)
        at javax.swing.plaf.basic.BasicComboPopup$1.processMouseEvent(BasicComboPopup.java:480)
        at java.awt.Component.processEvent(Component.java:5803)
        at java.awt.Container.processEvent(Container.java:2058)
        at java.awt.Component.dispatchEventImpl(Component.java:4410)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4240)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
        at java.awt.Container.dispatchEventImpl(Container.java:2102)
        at java.awt.Window.dispatchEventImpl(Window.java:2429)
        at java.awt.Component.dispatchEvent(Component.java:4240)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

Merci pour votre aide c tres urgent!!!