I'm trying to use com.izforge.izpack.util.NotEmptyValidator or com.izforge.izpack.util.RegularExpressionValidator in a UserInputPanel, but when the field is not valid, I got an exception (see below).
This is the userInputSpec.xml:
<userInput>
<panel order="0">
<createForPack name="Documentation server" />
<field type="title" txt="HTTP configuration" bold="true" size="1" />
<field type="divider" align="top"/>
<field type="text" variable="JETTY_PORT">
<description align="left" txt="The HTTP port used in the documentation server" id="description.text"/>
<spec txt="Enter a HTTP port number:" id="text.label" size="4" set="8080"/>
<validator class="com.izforge.izpack.util.NotEmptyValidator" txt="Invalid HTTP port">
</validator>
<!--
<validator class="com.izforge.izpack.util.RegularExpressionValidator" txt="Invalid HTTP port">
<param
name="pattern"
value="[0-9][0-9][0-9][0-9]"
/>
</validator>
-->
</field>
<field type="space"/>
<field type="divider" align="bottom"/>
</panel>
</userInput>

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at com.izforge.izpack.panels.UserInputPanel.showMessageDialog(UserInputPanel.java:3581)
at com.izforge.izpack.panels.UserInputPanel.showWarningMessageDialog(UserInputPanel.java:3598)
at com.izforge.izpack.panels.UserInputPanel.readTextField(UserInputPanel.java:1629)
at com.izforge.izpack.panels.UserInputPanel.readInput(UserInputPanel.java:1010)
at com.izforge.izpack.panels.UserInputPanel.isValidated(UserInputPanel.java:838)
at com.izforge.izpack.installer.InstallerFrame.navigateNext(InstallerFrame.java:1552)
at com.izforge.izpack.installer.InstallerFrame.navigateNext(InstallerFrame.java:1543)
at com.izforge.izpack.installer.InstallerFrame$NavigationHandler.actionPerformed(InstallerFrame.java:1626)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$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.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
at java.awt.Component.processMouseEvent(Component.java:6038)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
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)