Index: trunk/src/org/openstreetmap/josm/gui/dialogs/properties/ListOfUsedTags.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/dialogs/properties/ListOfUsedTags.java	(revision 2659)
+++ trunk/src/org/openstreetmap/josm/gui/dialogs/properties/ListOfUsedTags.java	(revision 2660)
@@ -10,4 +10,5 @@
 
 import org.openstreetmap.josm.Main;
+import org.openstreetmap.josm.data.osm.DataSet;
 import org.openstreetmap.josm.data.osm.OsmPrimitive;
 import org.openstreetmap.josm.data.osm.event.AbstractDatasetChangedEvent;
@@ -56,5 +57,8 @@
         dirty = false;
         allData.clear();
-        addPrimitives(Main.main.getCurrentDataSet().allNonDeletedPrimitives());
+        DataSet currentDataset = Main.main.getCurrentDataSet();
+        if (currentDataset != null) {
+            addPrimitives(currentDataset.allNonDeletedPrimitives());
+        }
     }