Index: trunk/src/org/openstreetmap/josm/gui/layer/NativeScaleLayer.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/layer/NativeScaleLayer.java	(revision 9882)
+++ trunk/src/org/openstreetmap/josm/gui/layer/NativeScaleLayer.java	(revision 9883)
@@ -150,4 +150,6 @@
          */
         public Scale getSnapScale(double scale, double ratio, boolean floor) {
+            if (scales.isEmpty())
+                return null;
             int size = scales.size();
             Scale first = scales.get(0);