Index: Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Utils/GrassCoverErosionInwardsHelper.cs
===================================================================
diff -u -re5658f822fa85cab8e99cb3069867d3a87867386 -rd207738be4ce6f50f4e3e00839ea433acea10bbd
--- Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Utils/GrassCoverErosionInwardsHelper.cs	(.../GrassCoverErosionInwardsHelper.cs)	(revision e5658f822fa85cab8e99cb3069867d3a87867386)
+++ Ringtoets/GrassCoverErosionInwards/src/Ringtoets.GrassCoverErosionInwards.Utils/GrassCoverErosionInwardsHelper.cs	(.../GrassCoverErosionInwardsHelper.cs)	(revision d207738be4ce6f50f4e3e00839ea433acea10bbd)
@@ -19,6 +19,7 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Core.Common.Base.Geometry;
@@ -41,19 +42,25 @@
         /// <returns>A <see cref="Dictionary{K, V}"/> containing a <see cref="IList{T}"/> 
         /// of <see cref="GrassCoverErosionInwardsFailureMechanismSectionResult"/> objects 
         /// for each section name which has calculations.</returns>
+        /// <exception cref="ArgumentNullException">When any input parameter is <c>null</c>.</exception>
         public static Dictionary<string, IList<GrassCoverErosionInwardsCalculation>> CollectCalculationsPerSegment(
             IEnumerable<GrassCoverErosionInwardsFailureMechanismSectionResult> sectionResults,
             IEnumerable<GrassCoverErosionInwardsCalculation> calculations)
         {
-            var calculationsPerSegment = new Dictionary<string, IList<GrassCoverErosionInwardsCalculation>>();
+            if (sectionResults == null)
+            {
+                throw new ArgumentNullException("sectionResults");
+            }
 
-            if (sectionResults == null || calculations == null)
+            if (calculations == null)
             {
-                return calculationsPerSegment;
+                throw new ArgumentNullException("calculations");
             }
 
             SectionSegments[] sectionSegments = MakeSectionSegments(sectionResults);
 
+            var calculationsPerSegment = new Dictionary<string, IList<GrassCoverErosionInwardsCalculation>>();
+
             foreach (var calculation in calculations)
             {
                 FailureMechanismSection section = FindSectionForCalculation(sectionSegments, calculation);
@@ -74,15 +81,21 @@
         /// whose <see cref="FailureMechanismSection"/> are considered.</param>
         /// <param name="calculation">The <see cref="GrassCoverErosionInwardsCalculation"/>.</param>
         /// <returns>The containing <see cref="FailureMechanismSection"/>, or <c>null</c>.</returns>
+        /// <exception cref="ArgumentNullException">When any input parameter is <c>null</c>.</exception>
         public static FailureMechanismSection FailureMechanismSectionForCalculation(
             IEnumerable<GrassCoverErosionInwardsFailureMechanismSectionResult> sectionResults,
             GrassCoverErosionInwardsCalculation calculation)
         {
-            if (sectionResults == null || calculation == null)
+            if (sectionResults == null)
             {
-                return null;
+                throw new ArgumentNullException("sectionResults");
             }
 
+            if (calculation == null)
+            {
+                throw new ArgumentNullException("calculation");
+            }
+
             SectionSegments[] sectionSegments = MakeSectionSegments(sectionResults);
 
             return FindSectionForCalculation(sectionSegments, calculation);