Index: trunk/src/org/openstreetmap/josm/gui/layer/GpxLayer.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/layer/GpxLayer.java	(revision 17899)
+++ trunk/src/org/openstreetmap/josm/gui/layer/GpxLayer.java	(revision 17900)
@@ -529,5 +529,5 @@
     @Override
     public boolean isModified() {
-        return data.isModified();
+        return data != null && data.isModified();
     }