Index: /trunk/src/org/openstreetmap/josm/actions/mapmode/SelectAction.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/actions/mapmode/SelectAction.java	(revision 5173)
+++ /trunk/src/org/openstreetmap/josm/actions/mapmode/SelectAction.java	(revision 5174)
@@ -966,5 +966,5 @@
             return tr("Release the mouse button to select the objects in the rectangle.");
         else if (mode == Mode.move) {
-            final boolean canMerge = !getCurrentDataSet().getSelectedNodes().isEmpty();
+            final boolean canMerge = getCurrentDataSet()!=null && !getCurrentDataSet().getSelectedNodes().isEmpty();
             final String mergeHelp = canMerge ? (" " + tr("Ctrl to merge with nearest node.")) : "";
             return tr("Release the mouse button to stop moving.") + mergeHelp;