Index: trunk/src/org/openstreetmap/josm/io/DiffResultProcessor.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/DiffResultProcessor.java	(revision 7657)
+++ trunk/src/org/openstreetmap/josm/io/DiffResultProcessor.java	(revision 7658)
@@ -109,6 +109,11 @@
             monitor = NullProgressMonitor.INSTANCE;
         }
-        DataSet ds = primitives.iterator().next().getDataSet();
-        ds.beginUpdate();
+        DataSet ds = null;
+        if (!primitives.isEmpty()) {
+            ds = primitives.iterator().next().getDataSet();
+        }
+        if (ds != null) {
+            ds.beginUpdate();
+        }
         try {
             monitor.beginTask("Postprocessing uploaded data ...");
@@ -134,5 +139,7 @@
             return processed;
         } finally {
-            ds.endUpdate();
+            if (ds != null) {
+                ds.endUpdate();
+            }
             monitor.finishTask();
         }