Index: trunk/src/org/openstreetmap/josm/io/OsmImporter.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/OsmImporter.java	(revision 4799)
+++ trunk/src/org/openstreetmap/josm/io/OsmImporter.java	(revision 4800)
@@ -11,5 +11,4 @@
 
 import javax.swing.JOptionPane;
-import javax.swing.SwingUtilities;
 
 import org.openstreetmap.josm.Main;
@@ -68,4 +67,7 @@
     public void loadLayer(InputStream in, final File associatedFile, final String layerName, ProgressMonitor progressMonitor) throws IllegalDataException {
         final DataSet dataSet = parseDataSet(in, progressMonitor);
+        if (dataSet == null) {
+            throw new IllegalDataException(tr("Invalid dataset"));
+        }
         layer = createLayer(dataSet, associatedFile, layerName);
         postLayerTask = createPostLayerTask(dataSet, associatedFile, layerName);