Index: trunk/src/org/openstreetmap/josm/data/APIDataSet.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/APIDataSet.java	(revision 13163)
+++ trunk/src/org/openstreetmap/josm/data/APIDataSet.java	(revision 13164)
@@ -99,9 +99,12 @@
 
         for (OsmPrimitive osm :primitives) {
-            switch (APIOperation.of(osm)) {
-                case ADD: toAdd.add(osm); break;
-                case UPDATE: toUpdate.add(osm); break;
-                case DELETE: toDelete.add(osm); break;
-                default: Logging.trace("Ignored primitive {0}", osm);
+            APIOperation op = APIOperation.of(osm);
+            if (op != null) {
+                switch (op) {
+                    case ADD: toAdd.add(osm); break;
+                    case UPDATE: toUpdate.add(osm); break;
+                    case DELETE: toDelete.add(osm); break;
+                    default: Logging.trace("Ignored primitive {0} -> {1}", osm, op);
+                }
             }
         }