Index: /trunk/src/org/openstreetmap/josm/data/imagery/ImageryLayerInfo.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/imagery/ImageryLayerInfo.java	(revision 8823)
+++ /trunk/src/org/openstreetmap/josm/data/imagery/ImageryLayerInfo.java	(revision 8824)
@@ -238,4 +238,8 @@
 
     private boolean isSimilar(ImageryInfo iiA, ImageryInfo iiB) {
+        if (iiA == null)
+            return false;
+        if (!iiA.getImageryType().equals(iiB.getImageryType()))
+            return false;
         if (iiA.getId() != null && iiB.getId() != null) return iiA.getId().equals(iiB.getId());
         return isSimilar(iiA.getUrl(), iiB.getUrl());