Terracer Plugin gives NullPointerException

[malenki]

What steps will reproduce the problem?

1. create a new data layer in JOSM
2. draw a rectangular closed way
3. press shift+T (invoking Terracer plugin)
4. click [OK]

What is the expected result?

Way gets divided in two.

What happens instead?

Exception

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

tested with:
blank ~/.josm
r8952
java -version
openjdk version "1.8.0_66-internal"
OpenJDK Runtime Environment (build 1.8.0_66-internal-b01)
OpenJDK 64-Bit Server VM (build 25.66-b01, mixed mode)

Revision: 8952
Repository Root: http://josm.openstreetmap.de/svn
Relative URL: ^/trunk
Last Changed Author: Don-vip
Last Changed Date: 2015-10-27 14:03:41 +0100 (Tue, 27 Oct 2015)
Build-Date: 2015-10-27 13:05:26
URL: http://josm.openstreetmap.de/svn/trunk
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last Changed Rev: 8952

Identification: JOSM/1.5 (8952 de) Linux LMDE 2 Betsy
Memory Usage: 480 MB / 2222 MB (318 MB allocated, but free)
Java version: 1.8.0_66-internal, Oracle Corporation, OpenJDK 64-Bit Server VM
VM arguments: [-Dsun.java2d.opengl=false]
Dataset consistency test: No problems found

Plugins:
- terracer (31694)

Last errors/warnings:
- E: java.lang.NullPointerException

java.lang.NullPointerException
	at org.openstreetmap.josm.command.ChangePropertyCommand.executeCommand(ChangePropertyCommand.java:113)
	at org.openstreetmap.josm.command.SequenceCommand.executeCommand(SequenceCommand.java:53)
	at terracer.TerracerAction$1.executeCommand(TerracerAction.java:470)
	at org.openstreetmap.josm.data.UndoRedoHandler.addNoRedraw(UndoRedoHandler.java:43)
	at org.openstreetmap.josm.data.UndoRedoHandler.add(UndoRedoHandler.java:69)
	at terracer.TerracerAction.terraceBuilding(TerracerAction.java:428)
	at terracer.HouseNumberInputHandler.actionPerformed(HouseNumberInputHandler.java:294)
	at terracer.HouseNumberInputDialog.buttonAction(HouseNumberInputDialog.java:235)
	at org.openstreetmap.josm.gui.ExtendedDialog$1.actionPerformed(ExtendedDialog.java:327)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
	at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
	at javax.swing.plaf.basic.BasicRootPaneUI$Actions.actionPerformed(BasicRootPaneUI.java:208)
	at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1663)
	at javax.swing.JComponent.processKeyBinding(JComponent.java:2882)
	at javax.swing.KeyboardManager.fireBinding(KeyboardManager.java:307)
	at javax.swing.KeyboardManager.fireKeyboardAction(KeyboardManager.java:250)
	at javax.swing.JComponent.processKeyBindingsForAllComponents(JComponent.java:2974)
	at javax.swing.JComponent.processKeyBindings(JComponent.java:2966)
	at javax.swing.JComponent.processKeyEvent(JComponent.java:2845)
	at java.awt.Component.processEvent(Component.java:6312)
	at java.awt.Container.processEvent(Container.java:2236)
	at java.awt.Component.dispatchEventImpl(Component.java:4891)
	at java.awt.Container.dispatchEventImpl(Container.java:2294)
	at java.awt.Component.dispatchEvent(Component.java:4713)
	at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1954)
	at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:806)
	at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:1074)
	at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:945)
	at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:771)
	at java.awt.Component.dispatchEventImpl(Component.java:4762)
	at java.awt.Container.dispatchEventImpl(Container.java:2294)
	at java.awt.Window.dispatchEventImpl(Window.java:2750)
	at java.awt.Component.dispatchEvent(Component.java:4713)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
	at java.awt.EventQueue.access$500(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.awt.EventQueue$3.run(EventQueue.java:703)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
	at java.awt.EventQueue$4.run(EventQueue.java:731)
	at java.awt.EventQueue$4.run(EventQueue.java:729)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
	at org.GNOME.Accessibility.AtkWrapper$4.dispatchEvent(AtkWrapper.java:571)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:109)
	at java.awt.WaitDispatchSupport$2.run(WaitDispatchSupport.java:184)
	at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:229)
	at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:227)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.awt.WaitDispatchSupport.enter(WaitDispatchSupport.java:227)
	at java.awt.Dialog.show(Dialog.java:1084)
	at java.awt.Component.show(Component.java:1673)
	at java.awt.Component.setVisible(Component.java:1625)
	at java.awt.Window.setVisible(Window.java:1014)
	at java.awt.Dialog.setVisible(Dialog.java:1005)
	at org.openstreetmap.josm.gui.ExtendedDialog.setVisible(ExtendedDialog.java:502)
	at org.openstreetmap.josm.gui.ExtendedDialog.showDialog(ExtendedDialog.java:290)
	at terracer.TerracerAction.actionPerformed(TerracerAction.java:233)
	at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1663)
	at javax.swing.JComponent.processKeyBinding(JComponent.java:2882)
	at javax.swing.KeyboardManager.fireBinding(KeyboardManager.java:307)
	at javax.swing.KeyboardManager.fireKeyboardAction(KeyboardManager.java:263)
	at javax.swing.JComponent.processKeyBindingsForAllComponents(JComponent.java:2974)
	at javax.swing.JComponent.processKeyBindings(JComponent.java:2966)
	at javax.swing.JComponent.processKeyEvent(JComponent.java:2845)
	at java.awt.Component.processEvent(Component.java:6312)
...<snip>...

[Don-vip]

In 8961/josm:

fix #12019 - NPE with ChangePropertyCommand called on objects without dataset - regression from r8941