Index: Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/CombinationTypeConverter.cs
===================================================================
diff -u -rfe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf -rcf5fa63f05c1018cdb14d5c664fa21f26026150c
--- Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/CombinationTypeConverter.cs	(.../CombinationTypeConverter.cs)	(revision fe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/CombinationTypeConverter.cs	(.../CombinationTypeConverter.cs)	(revision cf5fa63f05c1018cdb14d5c664fa21f26026150c)
@@ -19,7 +19,8 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
-using Ringtoets.Common.Data.Exceptions;
+using System;
+using System.ComponentModel;
 using Ringtoets.Common.Data.IllustrationPoints;
 using HydraRingCombinationType = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.CombinationType;
 
@@ -36,20 +37,27 @@
         /// <param name="hydraRingCombinationType">The <see cref="HydraRingCombinationType"/>
         /// to convert.</param>
         /// <returns>The <see cref="CombinationType"/>.</returns>
-        /// <exception cref="IllustrationPointConversionException">Thrown when
+        /// <exception cref="InvalidEnumArgumentException">Thrown when
         /// <paramref name="hydraRingCombinationType"/> has an invalid value.</exception>
+        /// <exception cref="NotSupportedException">Thrown when a valid value of 
+        /// <paramref name="hydraRingCombinationType"/> cannot be converted.</exception>
         public static CombinationType Convert(HydraRingCombinationType hydraRingCombinationType)
         {
+            if (!Enum.IsDefined(typeof(HydraRingCombinationType), hydraRingCombinationType))
+            {
+                throw new InvalidEnumArgumentException(nameof(hydraRingCombinationType),
+                                                           (int)hydraRingCombinationType,
+                                                           typeof(HydraRingCombinationType));
+            }
+
             switch (hydraRingCombinationType)
             {
                 case HydraRingCombinationType.Or:
                     return CombinationType.Or;
                 case HydraRingCombinationType.And:
                     return CombinationType.And;
                 default:
-                    string errorMessage = $"The value of {(int) hydraRingCombinationType} for {nameof(hydraRingCombinationType)} " +
-                                          $"could not be converted into a {typeof(CombinationType)}.";
-                    throw new IllustrationPointConversionException(errorMessage);
+                    throw new NotSupportedException($"A value of {hydraRingCombinationType} is not supported.");
             }
         }
     }
Index: Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/FaultTreeIllustrationPointConverter.cs
===================================================================
diff -u -rfe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf -rcf5fa63f05c1018cdb14d5c664fa21f26026150c
--- Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/FaultTreeIllustrationPointConverter.cs	(.../FaultTreeIllustrationPointConverter.cs)	(revision fe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/FaultTreeIllustrationPointConverter.cs	(.../FaultTreeIllustrationPointConverter.cs)	(revision cf5fa63f05c1018cdb14d5c664fa21f26026150c)
@@ -21,10 +21,12 @@
 
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Linq;
 using Ringtoets.Common.Data.Exceptions;
 using Ringtoets.Common.Data.IllustrationPoints;
 using HydraRingFaultTreeIllustrationPoint = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.FaultTreeIllustrationPoint;
+using HydraRingCombinationType = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.CombinationType;
 
 namespace Ringtoets.Common.Service.IllustrationPoints
 {
@@ -52,14 +54,25 @@
                 throw new ArgumentNullException(nameof(hydraRingFaultTreeIllustrationPoint));
             }
 
-            CombinationType combinationType = CombinationTypeConverter.Convert(hydraRingFaultTreeIllustrationPoint.CombinationType);
-            IEnumerable<Stochast> stochasts = hydraRingFaultTreeIllustrationPoint
-                .Stochasts.Select(StochastConverter.Convert);
+            FaultTreeIllustrationPoint illustrationPoint;
+            try
+            {
+                CombinationType combinationType = CombinationTypeConverter.Convert(hydraRingFaultTreeIllustrationPoint.CombinationType);
+                IEnumerable<Stochast> stochasts = hydraRingFaultTreeIllustrationPoint
+                    .Stochasts.Select(StochastConverter.Convert);
 
-            return new FaultTreeIllustrationPoint(hydraRingFaultTreeIllustrationPoint.Name,
-                                                  hydraRingFaultTreeIllustrationPoint.Beta,
-                                                  stochasts,
-                                                  combinationType);
+                illustrationPoint = new FaultTreeIllustrationPoint(hydraRingFaultTreeIllustrationPoint.Name,
+                                                                   hydraRingFaultTreeIllustrationPoint.Beta,
+                                                                   stochasts,
+                                                                   combinationType);
+            }
+            catch (Exception e) when (e is NotSupportedException || e is InvalidEnumArgumentException)
+            {
+                string errorMessage = $"Could not convert the {typeof(HydraRingCombinationType)} into a {typeof(CombinationType)}.";
+                throw new IllustrationPointConversionException(errorMessage, e);
+            }
+
+            return illustrationPoint;
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/IllustrationPointNodeConverter.cs
===================================================================
diff -u -rc77ccbb8b26516270f36ef53110be573839f3470 -rcf5fa63f05c1018cdb14d5c664fa21f26026150c
--- Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/IllustrationPointNodeConverter.cs	(.../IllustrationPointNodeConverter.cs)	(revision c77ccbb8b26516270f36ef53110be573839f3470)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/IllustrationPoints/IllustrationPointNodeConverter.cs	(.../IllustrationPointNodeConverter.cs)	(revision cf5fa63f05c1018cdb14d5c664fa21f26026150c)
@@ -23,7 +23,7 @@
 using System.Linq;
 using Ringtoets.Common.Data.Exceptions;
 using Ringtoets.Common.Data.IllustrationPoints;
-using Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints;
+using HydraRingIIllustrationPoint = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.IIllustrationPoint;
 using HydraRingFaultTreeIllustrationPoint = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.FaultTreeIllustrationPoint;
 using HydraRingSubMechanismIllustrationPoint = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.SubMechanismIllustrationPoint;
 using HydraRingIllustrationPointTreeNode = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.IllustrationPointTreeNode;
@@ -56,13 +56,17 @@
                 throw new ArgumentNullException(nameof(hydraRingIllustrationPointTreeNode));
             }
 
-            IllustrationPointBase data = ConvertIllustrationPointTreeNodeData(hydraRingIllustrationPointTreeNode.Data);
+            IllustrationPointBase data;
 
-            if (data == null)
+            try
             {
+                data = ConvertIllustrationPointTreeNodeData(hydraRingIllustrationPointTreeNode.Data);
+            }
+            catch (NotSupportedException e)
+            {
                 string errorMessage = "An illustration point containing a Hydra ring data type of " +
                                       $"{hydraRingIllustrationPointTreeNode.Data.GetType()} is not supported.";
-                throw new IllustrationPointConversionException(errorMessage);
+                throw new IllustrationPointConversionException(errorMessage, e);
             }
 
             var illustrationPointNode = new IllustrationPointNode(data);
@@ -71,15 +75,33 @@
             return illustrationPointNode;
         }
 
-        private static IllustrationPointBase ConvertIllustrationPointTreeNodeData(IIllustrationPoint data)
+        /// <summary>
+        /// Creates a new instance of a <see cref="IllustrationPointBase"/> based on the
+        /// <paramref name="data"/>. 
+        /// </summary>
+        /// <param name="data">The <see cref="HydraRingIIllustrationPoint"/> to base the 
+        /// <see cref="IllustrationPointBase"/> to create on.</param>
+        /// <returns>A <see cref="IllustrationPointBase"/>, <c>null</c> when no appropriate
+        /// conversion was found.</returns>
+        /// <exception cref="IllustrationPointConversionException">Thrown when <paramref name="data"/>
+        /// could not be converted.</exception>
+        /// <exception cref="NotSupportedException">Thrown when no suitable conversion for <paramref name="data"/>
+        /// was found.</exception>
+        private static IllustrationPointBase ConvertIllustrationPointTreeNodeData(HydraRingIIllustrationPoint data)
         {
             var faultTreeIllustrationPoint = data as HydraRingFaultTreeIllustrationPoint;
+            if (faultTreeIllustrationPoint != null)
+            {
+                return FaultTreeIllustrationPointConverter.Convert(faultTreeIllustrationPoint);
+            }
+
             var subMechanismIllustrationPoint = data as HydraRingSubMechanismIllustrationPoint;
-            return faultTreeIllustrationPoint != null
-                       ? (IllustrationPointBase) FaultTreeIllustrationPointConverter.Convert(faultTreeIllustrationPoint)
-                       : (subMechanismIllustrationPoint != null
-                              ? SubMechanismIllustrationPointConverter.Convert(subMechanismIllustrationPoint)
-                              : null);
+            if (subMechanismIllustrationPoint != null)
+            {
+                return SubMechanismIllustrationPointConverter.Convert(subMechanismIllustrationPoint);
+            }
+
+            throw new NotSupportedException($"Cannot convert {data.GetType()}.");
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/CombinationTypeConverterTest.cs
===================================================================
diff -u -rfe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf -rcf5fa63f05c1018cdb14d5c664fa21f26026150c
--- Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/CombinationTypeConverterTest.cs	(.../CombinationTypeConverterTest.cs)	(revision fe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf)
+++ Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/CombinationTypeConverterTest.cs	(.../CombinationTypeConverterTest.cs)	(revision cf5fa63f05c1018cdb14d5c664fa21f26026150c)
@@ -19,8 +19,9 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
+using System.ComponentModel;
+using Core.Common.TestUtil;
 using NUnit.Framework;
-using Ringtoets.Common.Data.Exceptions;
 using Ringtoets.Common.Data.IllustrationPoints;
 using Ringtoets.Common.Service.IllustrationPoints;
 using HydraRingCombinationType = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.CombinationType;
@@ -31,22 +32,21 @@
     public class CombinationTypeConverterTest
     {
         [Test]
-        public void Convert_InvalidEnumValue_ThrowsIllustrationPointConversionException()
+        public void Convert_InvalidEnumValue_ThrowsInvalidEnumArgumentException()
         {
             // Call
             TestDelegate test = () => CombinationTypeConverter.Convert((HydraRingCombinationType) 99);
 
             // Assert
-            var exception = Assert.Throws<IllustrationPointConversionException>(test);
-            string message = $"The value of 99 for hydraRingCombinationType could not be converted into a {typeof(CombinationType)}.";
-            Assert.AreEqual(message, exception.Message);
+            const string message = "The value of argument 'hydraRingCombinationType' (99) is invalid for Enum type 'CombinationType'.";
+            TestHelper.AssertThrowsArgumentExceptionAndTestMessage<InvalidEnumArgumentException>(test, message);
         }
 
         [Test]
         [TestCase(HydraRingCombinationType.And, CombinationType.And)]
         [TestCase(HydraRingCombinationType.Or, CombinationType.Or)]
         public void Convert_HydraRingCombinationType_ReturnCombinationType(HydraRingCombinationType hydraRingCombinationType,
-                                                                           CombinationType expectedCombinationType)
+                                                                          CombinationType expectedCombinationType)
         {
             // Call
             CombinationType combinationType = CombinationTypeConverter.Convert(hydraRingCombinationType);
Index: Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/FaultTreeIllustrationPointConverterTest.cs
===================================================================
diff -u -rfe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf -rcf5fa63f05c1018cdb14d5c664fa21f26026150c
--- Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/FaultTreeIllustrationPointConverterTest.cs	(.../FaultTreeIllustrationPointConverterTest.cs)	(revision fe0220615a6da7fcf3d1d1ad910c1c5ea95b42bf)
+++ Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/FaultTreeIllustrationPointConverterTest.cs	(.../FaultTreeIllustrationPointConverterTest.cs)	(revision cf5fa63f05c1018cdb14d5c664fa21f26026150c)
@@ -93,8 +93,9 @@
 
             // Assert
             var exception = Assert.Throws<IllustrationPointConversionException>(call);
-            string expectedMessage = $"The value of 999999 for hydraRingCombinationType could not be converted into a {typeof(CombinationType)}.";
+            string expectedMessage = $"Could not convert the {typeof(HydraRingCombinationType)} into a {typeof(CombinationType)}.";
             Assert.AreEqual(expectedMessage, exception.Message);
+            Assert.IsInstanceOf<InvalidEnumArgumentException>(exception.InnerException);
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/IllustrationPointNodeConverterTest.cs
===================================================================
diff -u -rc77ccbb8b26516270f36ef53110be573839f3470 -rcf5fa63f05c1018cdb14d5c664fa21f26026150c
--- Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/IllustrationPointNodeConverterTest.cs	(.../IllustrationPointNodeConverterTest.cs)	(revision c77ccbb8b26516270f36ef53110be573839f3470)
+++ Ringtoets/Common/test/Ringtoets.Common.Service.Test/IllustrationPoints/IllustrationPointNodeConverterTest.cs	(.../IllustrationPointNodeConverterTest.cs)	(revision cf5fa63f05c1018cdb14d5c664fa21f26026150c)
@@ -26,8 +26,6 @@
 using Ringtoets.Common.Data.IllustrationPoints;
 using Ringtoets.Common.Data.TestUtil;
 using Ringtoets.Common.Service.IllustrationPoints;
-using CombinationType = Ringtoets.Common.Data.IllustrationPoints.CombinationType;
-using FaultTreeIllustrationPoint = Ringtoets.Common.Data.IllustrationPoints.FaultTreeIllustrationPoint;
 using HydraRingIllustrationPointTreeNode = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.IllustrationPointTreeNode;
 using HydraRingStochast = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.Stochast;
 using HydraRingFaultTreeIllustrationPoint = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.FaultTreeIllustrationPoint;
@@ -38,10 +36,6 @@
 using TestHydraRingFaultTreeIllustrationPoint = Ringtoets.HydraRing.Calculation.TestUtil.IllustrationPoints.TestFaultTreeIllustrationPoint;
 using HydraRingCombinationType = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.CombinationType;
 using HydraRingIIllustrationPoint = Ringtoets.HydraRing.Calculation.Data.Output.IllustrationPoints.IIllustrationPoint;
-using IllustrationPointResult = Ringtoets.Common.Data.IllustrationPoints.IllustrationPointResult;
-using Stochast = Ringtoets.Common.Data.IllustrationPoints.Stochast;
-using SubMechanismIllustrationPoint = Ringtoets.Common.Data.IllustrationPoints.SubMechanismIllustrationPoint;
-using SubMechanismIllustrationPointStochast = Ringtoets.Common.Data.IllustrationPoints.SubMechanismIllustrationPointStochast;
 
 namespace Ringtoets.Common.Service.Test.IllustrationPoints
 {
@@ -173,6 +167,12 @@
             var exception = Assert.Throws<IllustrationPointConversionException>(call);
             string expectedMessage = $"An illustration point containing a Hydra ring data type of {hydraRingIllustrationPointData.GetType()} is not supported.";
             Assert.AreEqual(expectedMessage, exception.Message);
+
+            string expectedMessageInnerException = $"Cannot convert {hydraRingIllustrationPointData.GetType()}.";
+            Exception innerException = exception.InnerException;
+            Assert.IsNotNull(innerException);
+            Assert.IsInstanceOf<NotSupportedException>(innerException);
+            Assert.AreEqual(expectedMessageInnerException, innerException.Message);
         }
 
         [Test]
@@ -201,6 +201,12 @@
             var exception = Assert.Throws<IllustrationPointConversionException>(call);
             string expectedMessage = $"An illustration point containing a Hydra ring data type of {typeof(TestHydraRingIllustrationPointData)} is not supported.";
             Assert.AreEqual(expectedMessage, exception.Message);
+
+            string expectedMessageInnerException = $"Cannot convert {typeof(TestHydraRingIllustrationPointData)}.";
+            Exception innerException = exception.InnerException;
+            Assert.IsNotNull(innerException);
+            Assert.IsInstanceOf<NotSupportedException>(innerException);
+            Assert.AreEqual(expectedMessageInnerException, innerException.Message);
         }
 
         private class TestHydraRingIllustrationPointData : HydraRingIIllustrationPoint {}