Index: trunk/src/org/openstreetmap/josm/data/imagery/WMTSTileSource.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/imagery/WMTSTileSource.java	(revision 8626)
+++ trunk/src/org/openstreetmap/josm/data/imagery/WMTSTileSource.java	(revision 8627)
@@ -181,5 +181,5 @@
                 // TODO: save layer information into ImageryInfo / ImageryPreferences?
             } else {
-                throw new IllegalArgumentException(); //user canceled operation
+                throw new IllegalArgumentException(tr("No layer selected")); //user canceled operation
             }
         } else if (layers.size() == 1) {