Index: Ringtoets/Common/src/Ringtoets.Common.IO/SoilProfile/IStochasticSoilModelTransformer.cs
===================================================================
diff -u -r15ba57d868f00dfd3d6b52ac2e03a202d47d0303 -r03fa491ac6713c77d10987a9ba1d0776dfdf82e9
--- Ringtoets/Common/src/Ringtoets.Common.IO/SoilProfile/IStochasticSoilModelTransformer.cs	(.../IStochasticSoilModelTransformer.cs)	(revision 15ba57d868f00dfd3d6b52ac2e03a202d47d0303)
+++ Ringtoets/Common/src/Ringtoets.Common.IO/SoilProfile/IStochasticSoilModelTransformer.cs	(.../IStochasticSoilModelTransformer.cs)	(revision 03fa491ac6713c77d10987a9ba1d0776dfdf82e9)
@@ -35,9 +35,7 @@
         /// stochastic soil model of type <typeparamref name="T"/>.
         /// </summary>
         /// <param name="stochasticSoilModel">The stochastic soil model to use in the transformation.</param>
-        /// <returns>A new <typeparamref name="T"/> based on the given data, or <c>null</c> when 
-        /// <paramref name="stochasticSoilModel"/> is not of a type that can be transformed to 
-        /// the mechanism specific <typeparamref name="T"/>.</returns>
+        /// <returns>A new <typeparamref name="T"/> based on the given data.</returns>
         /// <exception cref="ImportedDataTransformException">Thrown when transformation would not result
         /// in a valid transformed instance.</exception>
         T Transform(StochasticSoilModel stochasticSoilModel);
Index: Ringtoets/Piping/src/Ringtoets.Piping.IO/Importers/PipingStochasticSoilModelTransformer.cs
===================================================================
diff -u -r15ba57d868f00dfd3d6b52ac2e03a202d47d0303 -r03fa491ac6713c77d10987a9ba1d0776dfdf82e9
--- Ringtoets/Piping/src/Ringtoets.Piping.IO/Importers/PipingStochasticSoilModelTransformer.cs	(.../PipingStochasticSoilModelTransformer.cs)	(revision 15ba57d868f00dfd3d6b52ac2e03a202d47d0303)
+++ Ringtoets/Piping/src/Ringtoets.Piping.IO/Importers/PipingStochasticSoilModelTransformer.cs	(.../PipingStochasticSoilModelTransformer.cs)	(revision 03fa491ac6713c77d10987a9ba1d0776dfdf82e9)
@@ -39,7 +39,8 @@
         {
             if (stochasticSoilModel.FailureMechanismType != FailureMechanismType.Piping)
             {
-                return null;
+                throw new ImportedDataTransformException($"Stochastic soil model of failure mechanism type '{stochasticSoilModel.FailureMechanismType}' is not supported." +
+                                                         $"Only '{FailureMechanismType.Piping}' is supported.");
             }
 
             IEnumerable<PipingStochasticSoilProfile> pipingStochasticSoilProfiles = TransformStochasticSoilProfiles(stochasticSoilModel.StochasticSoilProfiles);
Index: Ringtoets/Piping/test/Ringtoets.Piping.IO.Test/Importers/PipingStochasticSoilModelTransformerTest.cs
===================================================================
diff -u -r15ba57d868f00dfd3d6b52ac2e03a202d47d0303 -r03fa491ac6713c77d10987a9ba1d0776dfdf82e9
--- Ringtoets/Piping/test/Ringtoets.Piping.IO.Test/Importers/PipingStochasticSoilModelTransformerTest.cs	(.../PipingStochasticSoilModelTransformerTest.cs)	(revision 15ba57d868f00dfd3d6b52ac2e03a202d47d0303)
+++ Ringtoets/Piping/test/Ringtoets.Piping.IO.Test/Importers/PipingStochasticSoilModelTransformerTest.cs	(.../PipingStochasticSoilModelTransformerTest.cs)	(revision 03fa491ac6713c77d10987a9ba1d0776dfdf82e9)
@@ -23,6 +23,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using NUnit.Framework;
+using Ringtoets.Common.IO.Exceptions;
 using Ringtoets.Common.IO.SoilProfile;
 using Ringtoets.Common.IO.SoilProfile.Schema;
 using Ringtoets.Piping.Data.SoilProfile;
@@ -45,17 +46,19 @@
 
         [Test]
         [TestCaseSource(nameof(InvalidFailureMechanismTypes))]
-        public void Transform_InvalidFailureMechanismType_ReturnsNull(FailureMechanismType failureMechanismType)
+        public void Transform_InvalidFailureMechanismType_ThrowsImportedDataTransformException(FailureMechanismType failureMechanismType)
         {
             // Setup
             var transformer = new PipingStochasticSoilModelTransformer();
             var soilModel = new StochasticSoilModel("some name", failureMechanismType);
 
             // Call
-            PipingStochasticSoilModel transformed = transformer.Transform(soilModel);
+            TestDelegate test = () => transformer.Transform(soilModel);
 
             // Assert
-            Assert.IsNull(transformed);
+            var exception = Assert.Throws<ImportedDataTransformException>(test);
+            Assert.AreEqual($"Stochastic soil model of failure mechanism type '{failureMechanismType}' is not supported." +
+                            $"Only '{FailureMechanismType.Piping}' is supported.", exception.Message);
         }
 
         private static IEnumerable<FailureMechanismType> InvalidFailureMechanismTypes()