Index: Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/GrassCoverErosionInwardsCalculation.cs
===================================================================
diff -u -r4909d5c5d2883b3c6974f2f3840bd55797e8b0bd -ra894ca6401da7f18b092ba73e48d1995e87d6d8f
--- Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/GrassCoverErosionInwardsCalculation.cs	(.../GrassCoverErosionInwardsCalculation.cs)	(revision 4909d5c5d2883b3c6974f2f3840bd55797e8b0bd)
+++ Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Data/GrassCoverErosionInwardsCalculation.cs	(.../GrassCoverErosionInwardsCalculation.cs)	(revision a894ca6401da7f18b092ba73e48d1995e87d6d8f)
@@ -84,8 +84,12 @@
 
             clone.Comments = (Comment) Comments.Clone();
             clone.InputParameters = (GrassCoverErosionInwardsInput) InputParameters.Clone();
-            clone.Output = (GrassCoverErosionInwardsOutput) Output.Clone();
 
+            if (clone.Output != null)
+            {
+                clone.Output = (GrassCoverErosionInwardsOutput) Output.Clone();
+            }
+
             return clone;
         }
     }