[Patch] NPE in WMS tab of "Add Imagery URL" dialog

[anonymous]

What steps will reproduce the problem?

1. In Imagery preferences dialog, click on the + icon to add a manual WMS server
2. Click on "Get Layers" button without changing the default URL
3. Validate the error popup
4. Go the TMS tab
5. Go back to the WMS tab

What is the expected result? Nothing

What happens instead? An NPE happens and is signaled to the user in an error window.

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

Repository Root: http://josm.openstreetmap.de/svn
Build-Date: 2011-09-05 01:31:49
Last Changed Author: bastiK
Revision: 4399
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Date: 2011-09-04 22:13:51 +0200 (Sun, 04 Sep 2011)
Last Changed Rev: 4399

Identification: JOSM/1.5 (4399 cs)
Memory Usage: 77 MB / 247 MB (37 MB allocated, but free)
Java version: 1.6.0_27, Sun Microsystems Inc., Java HotSpot(TM) Client VM
Operating system: Windows 7
Dataset consistency test: No problems found


java.lang.NullPointerException
	at org.openstreetmap.josm.gui.preferences.AddWMSLayerPanel.commaSepLayerList(AddWMSLayerPanel.java:283)
	at org.openstreetmap.josm.gui.preferences.AddWMSLayerPanel.buildGetMapUrl(AddWMSLayerPanel.java:274)
	at org.openstreetmap.josm.gui.preferences.AddWMSLayerPanel.access$800(AddWMSLayerPanel.java:68)
	at org.openstreetmap.josm.gui.preferences.AddWMSLayerPanel$6.stateChanged(AddWMSLayerPanel.java:228)
	at javax.swing.JTabbedPane.fireStateChanged(Unknown Source)
	at javax.swing.JTabbedPane$ModelListener.stateChanged(Unknown Source)
	at javax.swing.DefaultSingleSelectionModel.fireStateChanged(Unknown Source)
	at javax.swing.DefaultSingleSelectionModel.setSelectedIndex(Unknown Source)
	at javax.swing.JTabbedPane.setSelectedIndexImpl(Unknown Source)
	at javax.swing.JTabbedPane.setSelectedIndex(Unknown Source)
	at javax.swing.plaf.basic.BasicTabbedPaneUI$Handler.mousePressed(Unknown Source)
	at java.awt.Component.processMouseEvent(Unkn

[Don-vip]

I have updated the description to add reproduction steps.
Please find attached a patch that fixes this issue.