NullPointerException when loading WMS imagery layer

[mhohmann]

What steps will reproduce the problem?

1. Load some data (in my case, in Estonia).
2. Switch on an imagery layer (in my case, Estonia Ortho, which is WMS).

What is the expected result?

The imagery layer should be displayed.

What happens instead?

Nothing is displayed and JOSM issues a crash / bug message every few seconds.

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

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-06-14 22:25:40 +0200 (Tue, 14 Jun 2016)
Build-Date:2016-06-15 01:34:12
Revision:10377
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10377 en) Linux Ubuntu 16.04 LTS
Memory Usage: 291 MB / 910 MB (64 MB allocated, but free)
Java version: 1.8.0_91-b14, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Dataset consistency test: No problems found

Plugins:
- AddrInterpolation (32158)
- FixAddresses (32158)
- Mapillary (32158)
- OpeningHoursEditor (32158)
- PicLayer (32158)
- apache-commons (32158)
- apache-http (32158)
- buildings_tools (32158)
- download_along (32158)
- measurement (32158)
- reverter (32158)
- terracer (32158)
- utilsplugin2 (32158)
- walkingpapers (32158)

Tagging presets:
- https://josm.openstreetmap.de/josmfile?page=Presets/Light_sources&zip=1

Map paint styles:
- /data/Maps/Styles/standard.mapcss
- /data/Maps/Styles/tmc.mapcss
- http://github.com/bastik/mapcss-tools/raw/osm/mapnik2mapcss/osm-results/mapnik.zip
- http://josm.openstreetmap.de/josmfile?page=Styles/light_source&zip=1
- https://josm.openstreetmap.de/josmfile?page=Styles/Maxspeed&style&zip=1

Last errors/warnings:
- W: Old style SideButton usage for action org.openstreetmap.josm.plugins.mapillary.gui.MapillaryHistoryDialog$RedoAction@49220604
- W: Old style SideButton usage for action org.openstreetmap.josm.plugins.mapillary.gui.MapillaryFilterDialog$UpdateAction@53e469da
- W: Old style SideButton usage for action org.openstreetmap.josm.plugins.mapillary.gui.MapillaryFilterDialog$ResetAction@59572235
- W: Old style SideButton usage for action org.openstreetmap.josm.plugins.measurement.MeasurementDialog$1@346716fa
- E: org.openstreetmap.josm.tools.bugreport.ReportedException: java.lang.NullPointerException. Cause: java.lang.NullPointerException

OSM API: http://api.openstreetmap.org/api

=== REPORTED CRASH DATA ===
MapView#paintLayer:
 - layer: org.openstreetmap.josm.gui.layer.WMSLayer@6b0f32c
 - bounds: Bounds[58.3540984,26.7199537,58.355097,26.7223541]

=== STACK TRACE ===
Thread: AWT-EventQueue-0 (18) of main
java.lang.NullPointerException
	at org.openstreetmap.josm.gui.layer.AbstractTileSourceLayer.getScaleFactor(AbstractTileSourceLayer.java:295)
	at org.openstreetmap.josm.gui.layer.AbstractTileSourceLayer.getBestZoom(AbstractTileSourceLayer.java:305)
	at org.openstreetmap.josm.gui.layer.AbstractTileSourceLayer.paint(AbstractTileSourceLayer.java:1449)
	at org.openstreetmap.josm.gui.MapView.paintLayer(MapView.java:754)
	at org.openstreetmap.josm.gui.MapView.paint(MapView.java:825)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paint(JComponent.java:1065)
	at javax.swing.JComponent.paintToOffscreen(JComponent.java:5210)
	at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:290)
	at javax.swing.RepaintManager.paint(RepaintManager.java:1272)
	at javax.swing.JComponent._paintImmediately(JComponent.java:5158)
	at javax.swing.JComponent.paintImmediately(JComponent.java:4969)
	at javax.swing.RepaintManager$4.run(RepaintManager.java:831)
	at javax.swing.RepaintManager$4.run(RepaintManager.java:814)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789)
	at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738)
	at javax.swing.RepaintManager.access$1200(RepaintManager.java:64)
	at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
	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.awt.EventQueue.dispatchEvent(EventQueue.java:726)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

[Don-vip]

Closed as duplicate of #12964.