Index: trunk/src/org/openstreetmap/josm/actions/downloadtasks/DownloadOsmTask.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/downloadtasks/DownloadOsmTask.java	(revision 5653)
+++ trunk/src/org/openstreetmap/josm/actions/downloadtasks/DownloadOsmTask.java	(revision 5654)
@@ -4,4 +4,5 @@
 import static org.openstreetmap.josm.tools.I18n.tr;
 
+import java.awt.geom.Area;
 import java.io.IOException;
 import java.util.ArrayList;
@@ -266,5 +267,8 @@
                     targetLayer = getFirstDataLayer();
                 }
-                isUpdateData = targetLayer.data.getDataSourceArea().contains(currentBounds.asRect());
+                Area dataSourceArea = targetLayer.data.getDataSourceArea();
+                if (dataSourceArea != null) {
+                    isUpdateData = dataSourceArea.contains(currentBounds.asRect());
+                }
                 targetLayer.mergeFrom(dataSet);
                 computeBboxAndCenterScale();