Index: Ringtoets/Integration/src/Ringtoets.Integration.Forms/Merge/AssessmentSectionProviderDialog.cs
===================================================================
diff -u -r18de555608fde7d9bfcef1346ff811dac47255eb -rd1e995328e2e80a3b292492724112a5072d31ca3
--- Ringtoets/Integration/src/Ringtoets.Integration.Forms/Merge/AssessmentSectionProviderDialog.cs	(.../AssessmentSectionProviderDialog.cs)	(revision 18de555608fde7d9bfcef1346ff811dac47255eb)
+++ Ringtoets/Integration/src/Ringtoets.Integration.Forms/Merge/AssessmentSectionProviderDialog.cs	(.../AssessmentSectionProviderDialog.cs)	(revision d1e995328e2e80a3b292492724112a5072d31ca3)
@@ -25,6 +25,11 @@
 
         public bool SelectData(IEnumerable<AssessmentSection> assessmentSections)
         {
+            if (assessmentSections == null)
+            {
+                throw new ArgumentNullException(nameof(assessmentSections));
+            }
+
             SetComboBoxData(assessmentSections);
             Show();
 
Index: Ringtoets/Integration/src/Ringtoets.Integration.Forms/Merge/IMergeDataProvider.cs
===================================================================
diff -u -r0abc3d3c19968df4450672ef585b3262d00b3ff8 -rd1e995328e2e80a3b292492724112a5072d31ca3
--- Ringtoets/Integration/src/Ringtoets.Integration.Forms/Merge/IMergeDataProvider.cs	(.../IMergeDataProvider.cs)	(revision 0abc3d3c19968df4450672ef585b3262d00b3ff8)
+++ Ringtoets/Integration/src/Ringtoets.Integration.Forms/Merge/IMergeDataProvider.cs	(.../IMergeDataProvider.cs)	(revision d1e995328e2e80a3b292492724112a5072d31ca3)
@@ -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 Ringtoets.Common.Data.FailureMechanism;
 using Ringtoets.Integration.Data;
@@ -45,6 +46,8 @@
         /// </summary>
         /// <param name="assessmentSections">The collection of assessment sections to select from.</param>
         /// <returns>Indicator whether selection succeeded.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="assessmentSections"/>
+        /// is <c>null</c>.</exception>
          bool SelectData(IEnumerable<AssessmentSection> assessmentSections);
     }
 }
\ No newline at end of file
Index: Ringtoets/Integration/test/Ringtoets.Integration.Forms.Test/Merge/AssessmentSectionProviderDialogTest.cs
===================================================================
diff -u -r18de555608fde7d9bfcef1346ff811dac47255eb -rd1e995328e2e80a3b292492724112a5072d31ca3
--- Ringtoets/Integration/test/Ringtoets.Integration.Forms.Test/Merge/AssessmentSectionProviderDialogTest.cs	(.../AssessmentSectionProviderDialogTest.cs)	(revision 18de555608fde7d9bfcef1346ff811dac47255eb)
+++ Ringtoets/Integration/test/Ringtoets.Integration.Forms.Test/Merge/AssessmentSectionProviderDialogTest.cs	(.../AssessmentSectionProviderDialogTest.cs)	(revision d1e995328e2e80a3b292492724112a5072d31ca3)
@@ -136,6 +136,27 @@
         }
 
         [Test]
+        public void SelectData_AssessmentSectionsNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var dialogParent = mocks.Stub<IWin32Window>();
+            mocks.ReplayAll();
+
+            using (var dialog = new AssessmentSectionProviderDialog(dialogParent))
+            {
+                // Call
+                TestDelegate call = () => dialog.SelectData(null);
+
+                // Assert
+                var exception = Assert.Throws<ArgumentNullException>(call);
+                Assert.AreEqual("assessmentSections", exception.ParamName);
+            }
+
+            mocks.VerifyAll();
+        }
+
+        [Test]
         public void SelectData_WithEmptyAssessmentSections_SetsDataOnDialog()
         {
             // Setup
@@ -204,7 +225,7 @@
 
                 var comboBox = (ComboBox) new ComboBoxTester("assessmentSectionComboBox", dialog).TheObject;
                 var dataGridView = (DataGridView) new ControlTester("dataGridView").TheObject;
-                
+
                 // Precondition 
                 AssessmentSection defaultSelectedAssessmentSection = assessmentSections[0];
                 Assert.AreSame(defaultSelectedAssessmentSection, comboBox.SelectedItem);