Erro ao chamar jComboBox1.removeallitems();

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at spiido.packs.jComboBox1ActionPerformed(packs.java:336)
        at spiido.packs.access$200(packs.java:22)
        at spiido.packs$2.actionPerformed(packs.java:251)
        at javax.swing.JComboBox.fireActionEvent(JComboBox.java:1240)
        at javax.swing.JComboBox.contentsChanged(JComboBox.java:1311)
        at javax.swing.JComboBox.intervalRemoved(JComboBox.java:1331)
        at javax.swing.AbstractListModel.fireIntervalRemoved(AbstractListModel.java:161)
        at javax.swing.DefaultComboBoxModel.removeAllElements(DefaultComboBoxModel.java:169)
        at javax.swing.JComboBox.removeAllItems(JComboBox.java:751)
        at spiido.packs.RefreshActionPerformed(packs.java:342)
        at spiido.packs.access$400(packs.java:22)
        at spiido.packs$4.actionPerformed(packs.java:264)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6216)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5981)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4583)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4556)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4220)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4150)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2475)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
CONSTRUÍDO COM SUCESSO (tempo total: 13 segundos)

selecionado = jComboBox1.getSelectedItem().toString();

private void jComboBox1ActionPerformed(java.awt.event.ActionEvent evt) {                                           
  selecionado = jComboBox1.getSelectedItem().toString();
  jComboBox2.removeAllItems();
  numerosdosepis(selecionado);
    }

private void RefreshActionPerformed(java.awt.event.ActionEvent evt) {                                        
        jComboBox1.removeAllItems();
        conexaoe();        
        
}