Index: DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/CsvExportData.cs
===================================================================
diff -u -r4384 -r4388
--- DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/CsvExportData.cs	(.../CsvExportData.cs)	(revision 4384)
+++ DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/CsvExportData.cs	(.../CsvExportData.cs)	(revision 4388)
@@ -220,7 +220,7 @@
             string fullFilename = DamProject.ProjectWorkingPath;
             if (string.IsNullOrEmpty(CalculationSubDir))
             {
-                throw new ArgumentNullException(nameof(CalculationSubDir));
+                throw new CsvExporterException(nameof(CalculationSubDir) + " is null or empty.");
             }
 
             fullFilename = Path.Combine(fullFilename, CalculationSubDir);
@@ -1635,7 +1635,8 @@
     {
         get
         {
-            if (damFailureMechanismeCalculationSpecification.FailureMechanismSystemType == FailureMechanismSystemType.Piping)
+            if (damFailureMechanismeCalculationSpecification != null &&
+                damFailureMechanismeCalculationSpecification.FailureMechanismSystemType == FailureMechanismSystemType.Piping)
             {
                 return damFailureMechanismeCalculationSpecification.PipingModelType;
             }
Index: DamClients/DamUI/trunk/src/Dam/Deltares.Dam.Tests/CsvExporterTest.cs
===================================================================
diff -u -r4070 -r4388
--- DamClients/DamUI/trunk/src/Dam/Deltares.Dam.Tests/CsvExporterTest.cs	(.../CsvExporterTest.cs)	(revision 4070)
+++ DamClients/DamUI/trunk/src/Dam/Deltares.Dam.Tests/CsvExporterTest.cs	(.../CsvExporterTest.cs)	(revision 4388)
@@ -36,6 +36,15 @@
         {
             Assert.That(() => new CsvExporter<CsvExportData>(null, null), Throws.InstanceOf<CsvExporterException>());
         }
+        
+        [Test]
+        public void ThrowWhenCalculationSubDirIsNull()
+        {
+            var exportData = new CsvExportData("locatioName", "scenarioName");
+            exportData.BaseFileName = "base";
+            exportData.CalculationSubDir = "";
+            Assert.That(() => exportData.GetDesignResultFile(), Throws.InstanceOf<CsvExporterException>());
+        }
 
         [Test]
         public void ThrowWhenFileNameIsNullOrEmpty()
Index: DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/DamEngineIo/FillDamUiFromXmlOutput.cs
===================================================================
diff -u -r4384 -r4388
--- DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/DamEngineIo/FillDamUiFromXmlOutput.cs	(.../FillDamUiFromXmlOutput.cs)	(revision 4384)
+++ DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/DamEngineIo/FillDamUiFromXmlOutput.cs	(.../FillDamUiFromXmlOutput.cs)	(revision 4388)
@@ -36,6 +36,15 @@
 namespace Deltares.Dam.Data.DamEngineIo;
 
 /// <summary>
+/// Exception class for FillDamUiFromXmlOutput 
+/// </summary>
+public class FillDamUiFromXmlOutputException : ApplicationException
+{
+    public FillDamUiFromXmlOutputException(string message)
+        : base(message) {}
+}
+
+/// <summary>
 /// Class to support the conversion of XmlOutput (as provided by the Engine) to DamUI objects.
 /// </summary>
 public class FillDamUiFromXmlOutput
@@ -431,12 +440,12 @@
         if (string.IsNullOrEmpty(desResult.CalculationSubDir) && (desResult.CalculationResult != CalculationResult.RunFailed) &&
             (desResult.CalculationResult != CalculationResult.UnexpectedError))
         {
-            throw new ArgumentNullException(nameof(desResult.CalculationSubDir));
+            throw new FillDamUiFromXmlOutputException(nameof(desResult.CalculationSubDir) + " is null or empty.");
         }
 
         if (string.IsNullOrEmpty(desResult.BaseFileName))
         {
-            throw new ArgumentNullException(nameof(desResult.BaseFileName));
+            throw new FillDamUiFromXmlOutputException(nameof(desResult.BaseFileName) + " is null or empty.");
         }
 
         if ((desResult.CalculationResult != CalculationResult.RunFailed)  &&