Index: trunk/src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java	(revision 9649)
+++ trunk/src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java	(revision 9656)
@@ -444,9 +444,13 @@
     public void setKeys(TagMap keys) {
         Map<String, String> originalKeys = getKeys();
-        String[] arr = keys.getTagsArray();
-        if (arr.length == 0) {
+        if (keys == null) {
             this.keys = null;
         } else {
-            this.keys = arr;
+            String[] arr = keys.getTagsArray();
+            if (arr.length == 0) {
+                this.keys = null;
+            } else {
+                this.keys = arr;
+            }
         }
         keysChangedImpl(originalKeys);