NPE when removing DataLayer while SegmentToKeepSelectionDialog opened

[Bjoeni]

1. split an uploaded way
2. keep dialog open that asks which segment should keep the history of the way
3. remove data layer
4. close dialog
5. NPE
6. no further splitting possible in this session because "another split operation is already in progress"

   Revision:17921
   Is-Local-Build:true
   Build-Date:2021-06-11 22:35:30
   
   Identification: JOSM/1.5 (17921 SVN en) Windows 10 64-Bit
   OS Build number: Windows 10 Home 2009 (21390)
   Memory Usage: 230 MB / 4028 MB (47 MB allocated, but free)
   Java version: 15.0.1+9-18, Oracle Corporation, OpenJDK 64-Bit Server VM
   Look and Feel: com.formdev.flatlaf.FlatDarkLaf
   Screen: \Display0 1920×1080 (scaling 1.00×1.00) \Display1 2560×1440 (scaling 1.00×1.00)
   Maximum Screen Size: 2560×1440
   Best cursor sizes: 16×16→32×32, 32×32→32×32
   System property file.encoding: UTF-8
   System property sun.jnu.encoding: Cp1252
   Locale info: en_DE
   Numbers with default locale: 1234567890 -> 1234567890
   VM arguments: [-agentlib:jdwp=transport=dt_socket,suspend=y,address=localhost:52574, -javaagent:C:\Users\nburc\eclipse\java-2021-03\eclipse\configuration\org.eclipse.osgi\222\0\.cp\lib\javaagent-shaded.jar, -Dfile.encoding=UTF-8]
   Program arguments: [--debug]
   
   Plugins:
   + BusRouteMaintenance (1619878317)
   + InfoMode (35543)
   + apache-commons (35524)
   + flatlaf (35734)
   + photo_geotagging (35738)
   + photoadjust (35770)
   
   Last errors/warnings:
   - 00333.768 E: Failed to locate image 'Waypoint'
   - 00667.798 E: Failed to locate image 'Waypoint'
   - 00667.799 E: Failed to locate image 'Waypoint'
   - 00672.860 E: Failed to locate image 'Waypoint'
   - 00672.861 E: Failed to locate image 'Waypoint'
   - 00781.662 E: Failed to locate image 'Waypoint'
   - 00781.663 E: Failed to locate image 'Waypoint'
   - 00781.671 E: Failed to locate image 'Waypoint'
   - 00781.672 E: Failed to locate image 'Waypoint'
   - 01987.839 E: Handled by bug report queue: java.lang.NullPointerException: Cannot invoke "org.openstreetmap.josm.data.osm.DataSet.setHighlightedWaySegments(java.util.Collection)" because the return value of "org.openstreetmap.josm.data.osm.Way.getDataSet()" is null
   
   
   
   === REPORTED CRASH DATA ===
   BugReportExceptionHandler#handleException:
   No data collected.
   
   Warning issued by: BugReportExceptionHandler#handleException
   
   === STACK TRACE ===
   Thread: AWT-EventQueue-0 (25) of main
   java.lang.NullPointerException: Cannot invoke "org.openstreetmap.josm.data.osm.DataSet.setHighlightedWaySegments(java.util.Collection)" because the return value of "org.openstreetmap.josm.data.osm.Way.getDataSet()" is null
   	at org.openstreetmap.josm.actions.SplitWayAction$SegmentToKeepSelectionDialog.setHighlightedWaySegments(SplitWayAction.java:212)
   	at org.openstreetmap.josm.actions.SplitWayAction$SegmentToKeepSelectionDialog.setVisible(SplitWayAction.java:223)
   	at org.openstreetmap.josm.gui.ExtendedDialog.buttonAction(ExtendedDialog.java:393)
   	at org.openstreetmap.josm.actions.SplitWayAction$SegmentToKeepSelectionDialog.buttonAction(SplitWayAction.java:233)
   	at org.openstreetmap.josm.gui.ExtendedDialog$1.actionPerformed(ExtendedDialog.java:381)
   	at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
   	at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
   	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.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
   	at java.desktop/java.awt.Component.processMouseEvent(Component.java:6614)
   	at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
   	at java.desktop/java.awt.Component.processEvent(Component.java:6379)
   	at java.desktop/java.awt.Container.processEvent(Container.java:2263)
   	at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4990)
   	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
   	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
   	at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4919)
   	at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4548)
   	at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4489)
   	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
   	at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2769)
   	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
   	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
   	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
   	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
   	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
   	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
   	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
   	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
   	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
   	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
   	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)
   

[Bjoeni]

Closed as duplicate of #20935.

Will be fixed in the referenced ticket.