Crash when removing layer above slippymap

[orrc]

What steps will reproduce the problem?

1. Have the slippymap plugin active
2. Open a .osm file
3. The .osm is rendered, with the slippymap layer beneath
4. In Layers, select the .osm layer and press the "Delete layer" button

What is the expected result?
The loaded layer is removed, leaving only the underlying slippy map.

What happens instead?
Crash.

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

Build-Date: 2009-12-13 02:31:40
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Author: jttt
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last Changed Date: 2009-12-12 21:25:10 +0100 (Sat, 12 Dec 2009)
Last Changed Rev: 2623
Repository Root: http://josm.openstreetmap.de/svn
Revision: 2623

Memory Usage: 63 MB / 63 MB (10 MB allocated, but free)
Java version: 1.5.0_20


Plugins: slippymap
Plugin slippymap Version: 19070

java.lang.NullPointerException
	at org.openstreetmap.josm.data.osm.event.DatasetEventManager.activeLayerChange(DatasetEventManager.java:71)
	at org.openstreetmap.josm.gui.MapView.fireActiveLayerChanged(MapView.java:107)
	at org.openstreetmap.josm.gui.MapView.removeLayer(MapView.java:327)
	at org.openstreetmap.josm.Main.removeLayer(Main.java:188)
	at org.openstreetmap.josm.gui.dialogs.LayerListDialog$DeleteLayerAction.actionPerformed(LayerListDialog.java:313)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1882)
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2202)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
	at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:231)
	at java.awt.Component.processMouseEvent(Component.java:5602)
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3135)
	at java.awt.Component.processEvent(Component.java:5367)
	at java.awt.Container.processEvent(Container.java:2010)
	at java.awt.Component.dispatchEventImpl(Component.java:4068)
	at java.awt.Container.dispatchEventImpl(Container.java:2068)
	at java.awt.Component.dispatchEvent(Component.java:3903)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4256)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3936)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3866)
	at java.awt.Container.dispatchEventImpl(Container.java:2054)
	at java.awt.Window.dispatchEventImpl(Window.java:1801)
	at java.awt.Component.dispatchEvent(Component.java:3903)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
	at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:269)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:176)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

[anonymous]

Closed as duplicate of #4159.