Index: trunk/src/org/openstreetmap/josm/io/session/OsmDataSessionExporter.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/session/OsmDataSessionExporter.java	(revision 7069)
+++ trunk/src/org/openstreetmap/josm/io/session/OsmDataSessionExporter.java	(revision 7070)
@@ -56,7 +56,4 @@
     }
 
-    public OsmDataSessionExporter() {
-    }
-
     @Override
     public Collection<Layer> getDependencies() {
Index: trunk/src/org/openstreetmap/josm/io/session/SessionWriter.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/session/SessionWriter.java	(revision 7069)
+++ trunk/src/org/openstreetmap/josm/io/session/SessionWriter.java	(revision 7070)
@@ -28,8 +28,4 @@
 import javax.xml.transform.stream.StreamResult;
 
-import org.w3c.dom.Document;
-import org.w3c.dom.Element;
-import org.w3c.dom.Text;
-
 import org.openstreetmap.josm.Main;
 import org.openstreetmap.josm.data.coor.EastNorth;
@@ -45,4 +41,7 @@
 import org.openstreetmap.josm.tools.MultiMap;
 import org.openstreetmap.josm.tools.Utils;
+import org.w3c.dom.Document;
+import org.w3c.dom.Element;
+import org.w3c.dom.Text;
 
 public class SessionWriter {
@@ -80,5 +79,5 @@
 
     private final List<Layer> layers;
-    private final int active; 
+    private final int active;
     private final Map<Layer, SessionLayerExporter> exporters;
     private final MultiMap<Layer, Layer> dependencies;
@@ -91,5 +90,5 @@
      * @param layers The ordered list of layers to save
      * @param active The index of active layer in {@code layers} (starts to 0). Ignored if set to -1
-     * @param exporters The exprters to use to save layers
+     * @param exporters The exporters to use to save layers
      * @param zip {@code true} if a joz archive has to be created, {@code false otherwise}
      * @since 6271
@@ -208,5 +207,5 @@
             }
             Set<Layer> deps = dependencies.get(layer);
-            if (!deps.isEmpty()) {
+            if (deps != null && !deps.isEmpty()) {
                 List<Integer> depsInt = new ArrayList<>();
                 for (Layer depLayer : deps) {
@@ -247,5 +246,5 @@
     }
 
-    public void write (OutputStream out) throws IOException {
+    public void write(OutputStream out) throws IOException {
         if (zip) {
             zipOut = new ZipOutputStream(new BufferedOutputStream(out));