error after deleting layer

[didier2020]

What steps will reproduce the problem?

1. work with josm
2. delete layer

What is the expected result?
no layer

What happens instead?
popup with error

Please provide any additional information below. Attach a screenshot if
possible.

Repository Root: http://josm.openstreetmap.de/svn
Build-Date: 2013-05-08 01:34:29
Last Changed Author: stoecker
Revision: 5939
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Date: 2013-05-07 14:05:08 +0200 (Tue, 07 May 2013)
Last Changed Rev: 5939

Identification: JOSM/1.5 (5939 fr) Linux Debian GNU/Linux 6.0.7 (squeeze)
Memory Usage: 1131 MB / 1820 MB (214 MB allocated, but free)
Java version: 1.6.0_26, Sun Microsystems Inc., Java HotSpot(TM) 64-Bit Server VM
VM arguments: [-Xmx2048M]

Plugin: cadastre-fr (29526)
Plugin: geotools (29435)
Plugin: jts (29435)
Plugin: poly (29435)
Plugin: proj4j (29435)
Plugin: tag2link (29461)
Plugin: todo (29155)
Plugin: utilsplugin2 (29435)
Plugin: wikipedia (29523)

java.lang.NullPointerException
	at org.openstreetmap.josm.gui.dialogs.ValidatorDialog$SelectionWatch.valueChanged(ValidatorDialog.java:501)
	at javax.swing.JTree.fireValueChanged(JTree.java:2820)
	at javax.swing.JTree$TreeSelectionRedirector.valueChanged(JTree.java:3191)
	at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(DefaultTreeSelectionModel.java:629)
	at javax.swing.tree.DefaultTreeSelectionModel.clearSelection(DefaultTreeSelectionModel.java:570)
	at javax.swing.tree.VariableHeightLayoutCache.rebuild(VariableHeightLayoutCache.java:740)
	at javax.swing.tree.VariableHeightLayoutCache.treeStructureChanged(VariableHeightLayoutCache.java:626)
	at javax.swing.plaf.basic.BasicTreeUI$Handler.treeStructureChanged(BasicTreeUI.java:3824)
	at javax.swing.tree.DefaultTreeModel.fireTreeStructureChanged(DefaultTreeModel.java:561)
	at javax.swing.tree.DefaultTreeModel.nodeStructureChanged(DefaultTreeModel.java:347)
	at javax.swing.tree.DefaultTreeModel.setRoot(DefaultTreeModel.java:117)
	at org.openstreetmap.josm.gui.dialogs.validator.ValidatorTreePanel.buildTree(ValidatorTreePanel.java:130)
	at org.openstreetmap.josm.gui.dialogs.validator.ValidatorTreePanel.setErrorList(ValidatorTreePanel.java:287)
	at org.openstreetmap.josm.gui.dialogs.ValidatorDialog.layerRemoved(ValidatorDialog.java:444)
	at org.openstreetmap.josm.gui.MapView.fireLayerRemoved(MapView.java:176)
	at org.openstreetmap.josm.gui.MapView.removeLayer(MapView.java:414)
	at org.openstreetmap.josm.Main.removeLayer(Main.java:296)
	at org.openstreetmap.josm.gui.dialogs.LayerListDialog$DeleteLayerAction.actionPerformed(LayerListDialog.java:397)
	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:6288)
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
	at java.awt.Component.processEvent(Component.java:6053)
	at java.awt.Container.processEvent(Container.java:2041)
	at java.awt.Component.dispatchEventImpl(Component.java:4651)
	at java.awt.Container.dispatchEventImpl(Container.java:2099)
	at java.awt.Component.dispatchEvent(Component.java:4481)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
	at java.awt.Container.dispatchEventImpl(Container.java:2085)
	at java.awt.Window.dispatchEventImpl(Window.java:2478)
	at java.awt.Component.dispatchEvent(Component.java:4481)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:643)
	at java.awt.EventQueue.access$000(EventQueue.java:84)
	at java.awt.EventQueue$1.run(EventQueue.java:602)
	at java.awt.EventQueue$1.run(EventQueue.java:600)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
	at java.awt.EventQueue$2.run(EventQueue.java:616)
	at java.awt.EventQueue$2.run(EventQueue.java:614)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:613)
	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)

[Don-vip]

In 5971/josm:

fix #8750 - NPE in ValidatorDialog