--- a/flys-artifacts/src/main/java/de/intevation/flys/artifacts/states/WDifferencesState.java	Wed Jan 18 16:21:30 2012 +0000
+++ b/flys-artifacts/src/main/java/de/intevation/flys/artifacts/states/WDifferencesState.java	Wed Jan 18 16:54:09 2012 +0000
@@ -13,12 +13,15 @@
 import de.intevation.flys.artifacts.FLYSArtifact;
 import de.intevation.flys.artifacts.StaticWKmsArtifact;
 import de.intevation.flys.artifacts.WINFOArtifact;
+import de.intevation.flys.artifacts.ChartArtifact;
 
 import de.intevation.flys.artifacts.math.WKmsOperation;
 
 import de.intevation.flys.artifacts.model.CalculationResult;
 import de.intevation.flys.artifacts.model.DataFacet;
 import de.intevation.flys.artifacts.model.DifferenceCurveFacet;
+import de.intevation.flys.artifacts.model.EmptyFacet;
+
 import de.intevation.flys.artifacts.model.FacetTypes;
 import de.intevation.flys.artifacts.model.WKms;
 import de.intevation.flys.artifacts.model.WQKms;
@@ -114,6 +117,11 @@
         List<Facet>  facets,
         Object       old
     ) {
+        if (artifact instanceof ChartArtifact) {
+            ChartArtifact chart = (ChartArtifact)artifact;
+            facets.add(new EmptyFacet());
+            return null;
+        }
         WINFOArtifact winfo = (WINFOArtifact) artifact;
         String id = getID();