Index: trunk/src/org/openstreetmap/josm/gui/dialogs/relation/RelationTreeModel.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/dialogs/relation/RelationTreeModel.java	(revision 1847)
+++ trunk/src/org/openstreetmap/josm/gui/dialogs/relation/RelationTreeModel.java	(revision 1848)
@@ -136,4 +136,7 @@
      */
     public void populate(Relation root) {
+        if (root == null) {
+            root = new Relation();
+        }
         this.root = root;
         fireRootReplacedEvent();