Steps to reproduce:
1.) Edit the RemoveUnusedImages_0.1.vmod
2.) Go to Game Piece Layouts → CounterBase → Soviet.png
3.) Right click and select “Duplicate this game piece Image”
4.) Uncaught Exception
2022-01-19 22:41:55,865 [10040-main] INFO VASSAL.launch.StartUp - Starting
2022-01-19 22:41:55,881 [10040-main] INFO VASSAL.launch.StartUp - OS Windows 10 10.0 amd64
2022-01-19 22:41:55,881 [10040-main] INFO VASSAL.launch.StartUp - Java version 17.0.1
2022-01-19 22:41:55,881 [10040-main] INFO VASSAL.launch.StartUp - Java home C:\Program Files\VASSAL-3.6.4\jre
2022-01-19 22:41:55,881 [10040-main] INFO VASSAL.launch.StartUp - VASSAL version 3.6.4
2022-01-19 22:41:56,037 [10040-AWT-EventQueue-0] INFO VASSAL.launch.ModuleManager - Manager
2022-01-19 22:42:32,465 [10040-SwingWorker-pool-2-thread-1] INFO VASSAL.launch.AbstractLaunchAction - Loading module file C:\Users\marcus\Documents\Spiele\CtoSx\_Vassal\RemoveUnusedImages\RemoveUnusedImages_0.1.vmod
2022-01-19 22:42:32,511 [10040-SwingWorker-pool-2-thread-1] INFO VASSAL.launch.TilingHandler - No images to tile.
2022-01-19 22:42:32,511 [10040-SwingWorker-pool-2-thread-1] INFO VASSAL.launch.AbstractLaunchAction - Loading module Remove Unused Images
2022-01-19 22:42:32,527 [10040-SwingWorker-pool-2-thread-1] INFO VASSAL.tools.io.ProcessLauncher - launching C:\Program Files\VASSAL-3.6.4\jre\bin\java -Xms512M -Xmx512M -Duser.home=C:\Users\marcus -Duser.dir=C:\Program Files\VASSAL-3.6.4 -cp lib\Vengine.jar VASSAL.launch.Player --load -- C:\Users\marcus\Documents\Spiele\CtoSx\_Vassal\RemoveUnusedImages\RemoveUnusedImages_0.1.vmod
2022-01-19 22:42:33,496 [5748-main] INFO VASSAL.launch.StartUp - Starting
2022-01-19 22:42:33,511 [5748-main] INFO VASSAL.launch.StartUp - OS Windows 10 10.0 amd64
2022-01-19 22:42:33,511 [5748-main] INFO VASSAL.launch.StartUp - Java version 17.0.1
2022-01-19 22:42:33,511 [5748-main] INFO VASSAL.launch.StartUp - Java home C:\Program Files\VASSAL-3.6.4\jre
2022-01-19 22:42:33,511 [5748-main] INFO VASSAL.launch.StartUp - VASSAL version 3.6.4
2022-01-19 22:42:33,511 [5748-main] INFO VASSAL.launch.Launcher - Player
2022-01-19 22:42:35,895 [5748-AWT-EventQueue-0] INFO VASSAL.build.GameModule - Remove Unused Images version 0.1
2022-01-19 22:42:38,646 [5748-AWT-EventQueue-0] INFO VASSAL.build.GameModule - Exiting
2022-01-19 22:42:44,626 [10040-SwingWorker-pool-2-thread-2] INFO VASSAL.launch.AbstractLaunchAction - Loading module file C:\Users\marcus\Documents\Spiele\CtoSx\_Vassal\RemoveUnusedImages\RemoveUnusedImages_0.1.vmod
2022-01-19 22:42:44,626 [10040-SwingWorker-pool-2-thread-2] INFO VASSAL.launch.TilingHandler - No images to tile.
2022-01-19 22:42:44,626 [10040-SwingWorker-pool-2-thread-2] INFO VASSAL.launch.AbstractLaunchAction - Loading module Remove Unused Images
2022-01-19 22:42:44,626 [10040-SwingWorker-pool-2-thread-2] INFO VASSAL.tools.io.ProcessLauncher - launching C:\Program Files\VASSAL-3.6.4\jre\bin\java -Xms512M -Xmx512M -Duser.home=C:\Users\marcus -Duser.dir=C:\Program Files\VASSAL-3.6.4 -cp lib\Vengine.jar VASSAL.launch.Editor --edit -- C:\Users\marcus\Documents\Spiele\CtoSx\_Vassal\RemoveUnusedImages\RemoveUnusedImages_0.1.vmod
2022-01-19 22:42:45,626 [976-main] INFO VASSAL.launch.StartUp - Starting
2022-01-19 22:42:45,642 [976-main] INFO VASSAL.launch.StartUp - OS Windows 10 10.0 amd64
2022-01-19 22:42:45,642 [976-main] INFO VASSAL.launch.StartUp - Java version 17.0.1
2022-01-19 22:42:45,642 [976-main] INFO VASSAL.launch.StartUp - Java home C:\Program Files\VASSAL-3.6.4\jre
2022-01-19 22:42:45,642 [976-main] INFO VASSAL.launch.StartUp - VASSAL version 3.6.4
2022-01-19 22:42:45,642 [976-main] INFO VASSAL.launch.Launcher - Editor
2022-01-19 22:42:47,960 [976-AWT-EventQueue-0] INFO VASSAL.build.GameModule - Remove Unused Images version 0.1
2022-01-19 22:42:58,919 [976-AWT-EventQueue-0] ERROR VASSAL.tools.ErrorDialog -
java.lang.NullPointerException: Cannot invoke "VASSAL.build.module.gamepieceimage.GamePieceLayout.getItem(String)" because "this.layout" is null
at VASSAL.build.module.gamepieceimage.GamePieceImage.rebuildInstances(GamePieceImage.java:470)
at VASSAL.build.module.gamepieceimage.GamePieceImage$DefnConfig.getConfigurer(GamePieceImage.java:175)
at VASSAL.configure.AutoConfigurer.createConfigurer(AutoConfigurer.java:206)
at VASSAL.configure.AutoConfigurer.<init>(AutoConfigurer.java:87)
at VASSAL.build.AbstractConfigurable.getConfigurer(AbstractConfigurable.java:212)
at VASSAL.configure.ConfigureTree$8.actionPerformed(ConfigureTree.java:894)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1972)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2313)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
at java.desktop/javax.swing.AbstractButton.doClick(AbstractButton.java:374)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1028)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1072)
at java.desktop/java.awt.Component.processMouseEvent(Component.java:6626)
at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3389)
at java.desktop/java.awt.Component.processEvent(Component.java:6391)
at java.desktop/java.awt.Container.processEvent(Container.java:2266)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5001)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2324)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4948)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4575)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4516)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2310)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2780)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4833)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:722)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:716)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:97)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:746)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:744)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:743)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)