Index: src/org/openstreetmap/josm/gui/preferences/AddWMSLayerPanel.java
===================================================================
--- src/org/openstreetmap/josm/gui/preferences/AddWMSLayerPanel.java	(revision 4465)
+++ src/org/openstreetmap/josm/gui/preferences/AddWMSLayerPanel.java	(working copy)
@@ -280,12 +280,14 @@
     private String commaSepLayerList() {
         StringBuilder b = new StringBuilder();
 
-        Iterator<LayerDetails> iterator = selectedLayers.iterator();
-        while (iterator.hasNext()) {
-            LayerDetails layerDetails = iterator.next();
-            b.append(layerDetails.ident);
-            if(iterator.hasNext()) {
-                b.append(",");
+        if (selectedLayers != null) {
+            Iterator<LayerDetails> iterator = selectedLayers.iterator();
+            while (iterator.hasNext()) {
+                LayerDetails layerDetails = iterator.next();
+                b.append(layerDetails.ident);
+                if(iterator.hasNext()) {
+                    b.append(",");
+                }
             }
         }