Index: Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Service/GrassCoverErosionInwardsCalculationService.cs
===================================================================
diff -u -r08adf25cc7efeb88759bcba90e9881466fbf60f9 -ra2816cf7e28f73c0ea8c9432cee533ace72543cc
--- Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Service/GrassCoverErosionInwardsCalculationService.cs	(.../GrassCoverErosionInwardsCalculationService.cs)	(revision 08adf25cc7efeb88759bcba90e9881466fbf60f9)
+++ Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Service/GrassCoverErosionInwardsCalculationService.cs	(.../GrassCoverErosionInwardsCalculationService.cs)	(revision a2816cf7e28f73c0ea8c9432cee533ace72543cc)
@@ -123,9 +123,10 @@
 
             double? dikeHeightOutput = null;
 
-            if (calculateDikeHeight && targetProbabiltyCalculationParser.Output != null)
+            if (calculateDikeHeight)
             {
-                dikeHeightOutput = targetProbabiltyCalculationParser.Output.Result;
+                TargetProbabilityCalculationOutput output = targetProbabiltyCalculationParser.Output;
+                dikeHeightOutput = output == null ? double.NaN : output.Result;
             }
 
             return new GrassCoverErosionInwardsCalculationServiceOutput(