Index: Ringtoets/WaveImpactAsphaltCover/src/Ringtoets.WaveImpactAsphaltCover.Forms/PresentationObjects/WaveImpactAsphaltCoverCalculationGroupContext.cs
===================================================================
diff -u -rf0792e734ef5296f2ffaae2ad36619a05d5bd9e3 -r2f2f5862ef2f51e6102511cb6c6de57fbaabe554
--- Ringtoets/WaveImpactAsphaltCover/src/Ringtoets.WaveImpactAsphaltCover.Forms/PresentationObjects/WaveImpactAsphaltCoverCalculationGroupContext.cs	(.../WaveImpactAsphaltCoverCalculationGroupContext.cs)	(revision f0792e734ef5296f2ffaae2ad36619a05d5bd9e3)
+++ Ringtoets/WaveImpactAsphaltCover/src/Ringtoets.WaveImpactAsphaltCover.Forms/PresentationObjects/WaveImpactAsphaltCoverCalculationGroupContext.cs	(.../WaveImpactAsphaltCoverCalculationGroupContext.cs)	(revision 2f2f5862ef2f51e6102511cb6c6de57fbaabe554)
@@ -68,7 +68,7 @@
 
         public override int GetHashCode()
         {
-            return base.GetHashCode() ^ Parent.GetHashCode();
+            return base.GetHashCode() ^ Parent?.GetHashCode() ?? 0;
         }
     }
 }
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