Index: DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/Routines2D.cs
===================================================================
diff -u -r4132 -r4172
--- DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/Routines2D.cs	(.../Routines2D.cs)	(revision 4132)
+++ DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/Routines2D.cs	(.../Routines2D.cs)	(revision 4172)
@@ -269,37 +269,41 @@
 
             while (index < polygon.CalcPoints.Count)
             {
-                deltaX = polygon[index].X - x;
-                deltaZ = polygon[index].Z - z;
-                absX = Math.Abs(deltaX);
-                absZ = Math.Abs(deltaZ);
-                if ((absX < epsilon) && (absZ < epsilon))
+                if (polygon[index] != null)
                 {
-                    UndoAddIfNeeded(polygon, pointAdded);
-                    return PointInPolygon.OnPolygonEdge;
-                }
+                    deltaX = polygon[index].X - x;
+                    deltaZ = polygon[index].Z - z;
+                    absX = Math.Abs(deltaX);
+                    absZ = Math.Abs(deltaZ);
+                    if ((absX < epsilon) && (absZ < epsilon))
+                    {
+                        UndoAddIfNeeded(polygon, pointAdded);
+                        return PointInPolygon.OnPolygonEdge;
+                    }
 
-                double al2 = Math.Atan2(deltaZ, deltaX);
-                double al3 = al2 - al1;
+                    double al2 = Math.Atan2(deltaZ, deltaX);
+                    double al3 = al2 - al1;
 
-                if (al3 < -Math.PI)
-                {
-                    al3 = al3 + (2.0 * Math.PI);
-                }
+                    if (al3 < -Math.PI)
+                    {
+                        al3 = al3 + (2.0 * Math.PI);
+                    }
 
-                if (al3 > Math.PI)
-                {
-                    al3 = al3 - (2.0 * Math.PI);
-                }
+                    if (al3 > Math.PI)
+                    {
+                        al3 = al3 - (2.0 * Math.PI);
+                    }
 
-                if (((Math.PI - al3) < epsilon) || ((Math.PI + al3) < epsilon))
-                {
-                    UndoAddIfNeeded(polygon, pointAdded);
-                    return PointInPolygon.OnPolygonEdge;
+                    if (((Math.PI - al3) < epsilon) || ((Math.PI + al3) < epsilon))
+                    {
+                        UndoAddIfNeeded(polygon, pointAdded);
+                        return PointInPolygon.OnPolygonEdge;
+                    }
+
+                    som = som + al3;
+                    al1 = al2;
                 }
 
-                som = som + al3;
-                al1 = al2;
                 index++;
             }