Index: /trunk/src/org/openstreetmap/josm/gui/MapView.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/MapView.java	(revision 2652)
+++ /trunk/src/org/openstreetmap/josm/gui/MapView.java	(revision 2653)
@@ -623,5 +623,5 @@
      */
     public void setActiveLayer(Layer layer) {
-        if (!layers.contains(layer))
+        if (layer != null && !layers.contains(layer))
             throw new IllegalArgumentException(tr("Layer ''{0}'' must be in list of layers", layer.toString()));