Index: trunk/src/org/openstreetmap/josm/data/osm/User.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/osm/User.java	(revision 13100)
+++ trunk/src/org/openstreetmap/josm/data/osm/User.java	(revision 13101)
@@ -70,5 +70,7 @@
 
         if (lastUser != null && lastUser.getId() == uid) {
-            lastUser.setPreferredName(name);
+            if (name != null) {
+                lastUser.setPreferredName(name);
+            }
             return lastUser;
         }