Index: trunk/src/org/openstreetmap/josm/actions/JoinAreasAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/JoinAreasAction.java	(revision 13634)
+++ trunk/src/org/openstreetmap/josm/actions/JoinAreasAction.java	(revision 13635)
@@ -547,10 +547,10 @@
                 commitCommands(tr("Move tags from ways to relations"));
 
-                List<Way> allWays = new ArrayList<>();
-                for (Multipolygon pol : result.polygons) {
-                    allWays.add(pol.outerWay);
-                    allWays.addAll(pol.innerWays);
-                }
-                if (ds != null) {
+                if (result.polygons != null && ds != null) {
+                    List<Way> allWays = new ArrayList<>();
+                    for (Multipolygon pol : result.polygons) {
+                        allWays.add(pol.outerWay);
+                        allWays.addAll(pol.innerWays);
+                    }
                     ds.setSelected(allWays);
                 }