Index: Riskeer/Integration/src/Riskeer.Integration.Forms/Merge/AssessmentSectionMergeDataProviderDialog.cs
===================================================================
diff -u -rce6893c628a4f5e22301b1d36269dd81a4fddb01 -re16379882e48c2d1a5bfac45250a3260cc72ac4d
--- Riskeer/Integration/src/Riskeer.Integration.Forms/Merge/AssessmentSectionMergeDataProviderDialog.cs	(.../AssessmentSectionMergeDataProviderDialog.cs)	(revision ce6893c628a4f5e22301b1d36269dd81a4fddb01)
+++ Riskeer/Integration/src/Riskeer.Integration.Forms/Merge/AssessmentSectionMergeDataProviderDialog.cs	(.../AssessmentSectionMergeDataProviderDialog.cs)	(revision e16379882e48c2d1a5bfac45250a3260cc72ac4d)
@@ -66,20 +66,15 @@
             InitializeDataGridView();
         }
 
-        public AssessmentSectionMergeData GetMergeData(IEnumerable<AssessmentSection> assessmentSections)
+        public AssessmentSectionMergeData GetMergeData(AssessmentSection assessmentSection)
         {
-            if (assessmentSections == null)
+            if (assessmentSection == null)
             {
-                throw new ArgumentNullException(nameof(assessmentSections));
+                throw new ArgumentNullException(nameof(assessmentSection));
             }
 
-            if (!assessmentSections.Any())
-            {
-                throw new ArgumentException($@"{nameof(assessmentSections)} must at least have one element.", nameof(assessmentSections));
-            }
+            SetDataGridViewData(assessmentSection);
 
-            SetDataGridViewData(assessmentSections.Single());
-
             if (ShowDialog() == DialogResult.OK)
             {
                 var constructionProperties = new AssessmentSectionMergeData.ConstructionProperties
@@ -105,7 +100,7 @@
                 };
                 constructionProperties.MergeSpecificFailurePaths.AddRange(GetSelectedSpecificFailurePathsToMerge());
 
-                return new AssessmentSectionMergeData(assessmentSections.Single(),
+                return new AssessmentSectionMergeData(assessmentSection,
                                                       constructionProperties);
             }
 
Index: Riskeer/Integration/src/Riskeer.Integration.Forms/Merge/IAssessmentSectionMergeDataProvider.cs
===================================================================
diff -u -rc36b47c2e1e8cf948767cca33f80ad735f370ad0 -re16379882e48c2d1a5bfac45250a3260cc72ac4d
--- Riskeer/Integration/src/Riskeer.Integration.Forms/Merge/IAssessmentSectionMergeDataProvider.cs	(.../IAssessmentSectionMergeDataProvider.cs)	(revision c36b47c2e1e8cf948767cca33f80ad735f370ad0)
+++ Riskeer/Integration/src/Riskeer.Integration.Forms/Merge/IAssessmentSectionMergeDataProvider.cs	(.../IAssessmentSectionMergeDataProvider.cs)	(revision e16379882e48c2d1a5bfac45250a3260cc72ac4d)
@@ -20,7 +20,6 @@
 // All rights reserved.
 
 using System;
-using System.Collections.Generic;
 using Riskeer.Integration.Data;
 using Riskeer.Integration.Data.Merge;
 
@@ -34,13 +33,10 @@
         /// <summary>
         /// Gets the data to merge.
         /// </summary>
-        /// <param name="assessmentSections">The collection of assessment sections to get the merge
-        /// data from.</param>
+        /// <param name="assessmentSection">The assessment section to get the merge data from.</param>
         /// <returns>The selected merge data.</returns>
-        /// <exception cref="ArgumentNullException">Thrown when <paramref name="assessmentSections"/>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="assessmentSection"/>
         /// is <c>null</c>.</exception>
-        /// <exception cref="ArgumentException">Thrown when <paramref name="assessmentSections"/>
-        /// contains no elements.</exception>
-        AssessmentSectionMergeData GetMergeData(IEnumerable<AssessmentSection> assessmentSections);
+        AssessmentSectionMergeData GetMergeData(AssessmentSection assessmentSection);
     }
 }
\ No newline at end of file
Index: Riskeer/Integration/src/Riskeer.Integration.Plugin/Merge/AssessmentSectionMerger.cs
===================================================================
diff -u -r48244f68eee25ef1d91701d82e4c4867f0252ffc -re16379882e48c2d1a5bfac45250a3260cc72ac4d
--- Riskeer/Integration/src/Riskeer.Integration.Plugin/Merge/AssessmentSectionMerger.cs	(.../AssessmentSectionMerger.cs)	(revision 48244f68eee25ef1d91701d82e4c4867f0252ffc)
+++ Riskeer/Integration/src/Riskeer.Integration.Plugin/Merge/AssessmentSectionMerger.cs	(.../AssessmentSectionMerger.cs)	(revision e16379882e48c2d1a5bfac45250a3260cc72ac4d)
@@ -135,7 +135,7 @@
                 return;
             }
 
-            AssessmentSectionMergeData mergeData = mergeDataProvider.GetMergeData(matchingAssessmentSections);
+            AssessmentSectionMergeData mergeData = mergeDataProvider.GetMergeData(matchingAssessmentSections.Single());
 
             if (mergeData == null)
             {
Index: Riskeer/Integration/test/Riskeer.Integration.Forms.Test/Merge/AssessmentSectionMergeDataProviderDialogTest.cs
===================================================================
diff -u -rce6893c628a4f5e22301b1d36269dd81a4fddb01 -re16379882e48c2d1a5bfac45250a3260cc72ac4d
--- Riskeer/Integration/test/Riskeer.Integration.Forms.Test/Merge/AssessmentSectionMergeDataProviderDialogTest.cs	(.../AssessmentSectionMergeDataProviderDialogTest.cs)	(revision ce6893c628a4f5e22301b1d36269dd81a4fddb01)
+++ Riskeer/Integration/test/Riskeer.Integration.Forms.Test/Merge/AssessmentSectionMergeDataProviderDialogTest.cs	(.../AssessmentSectionMergeDataProviderDialogTest.cs)	(revision e16379882e48c2d1a5bfac45250a3260cc72ac4d)
@@ -184,7 +184,7 @@
         }
 
         [Test]
-        public void GetMergeData_AssessmentSectionsNull_ThrowsArgumentNullException()
+        public void GetMergeData_AssessmentSectionNull_ThrowsArgumentNullException()
         {
             // Setup
             var mocks = new MockRepository();
@@ -194,32 +194,17 @@
             using (var dialog = new AssessmentSectionMergeDataProviderDialog(dialogParent))
             {
                 // Call
-                TestDelegate call = () => dialog.GetMergeData(null);
+                void Call() => dialog.GetMergeData(null);
 
                 // Assert
-                var exception = Assert.Throws<ArgumentNullException>(call);
-                Assert.AreEqual("assessmentSections", exception.ParamName);
+                var exception = Assert.Throws<ArgumentNullException>(Call);
+                Assert.AreEqual("assessmentSection", exception.ParamName);
             }
 
             mocks.VerifyAll();
         }
 
         [Test]
-        public void GetMergeData_WithEmptyAssessmentSections_ThrowsArgumentException()
-        {
-            // Setup
-            using (var dialogParent = new Form())
-            using (var dialog = new AssessmentSectionMergeDataProviderDialog(dialogParent))
-            {
-                // Call
-                TestDelegate call = () => dialog.GetMergeData(Enumerable.Empty<AssessmentSection>());
-
-                // Assert
-                TestHelper.AssertThrowsArgumentExceptionAndTestMessage<ArgumentException>(call, "assessmentSections must at least have one element.");
-            }
-        }
-
-        [Test]
         public void GetMergeData_WithAssessmentSection_SetsDataOnDialog()
         {
             // Setup
@@ -228,28 +213,23 @@
                 using (new FormTester(formName)) {}
             };
 
-            AssessmentSection[] assessmentSections =
-            {
-                TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths()
-            };
+            AssessmentSection assessmentSection = TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths();
 
             using (var dialogParent = new Form())
             using (var dialog = new AssessmentSectionMergeDataProviderDialog(dialogParent))
             {
                 // Call
-                dialog.GetMergeData(assessmentSections);
+                dialog.GetMergeData(assessmentSection);
 
                 // Assert
-                AssessmentSection expectedDefaultSelectedAssessmentSection = assessmentSections[0];
-
                 var dataGridView = (DataGridView) new ControlTester("dataGridView", dialog).TheObject;
                 DataGridViewRowCollection rows = dataGridView.Rows;
 
-                int expectedNrOfRows = expectedDefaultSelectedAssessmentSection.GetFailureMechanisms().Count() +
-                                       expectedDefaultSelectedAssessmentSection.SpecificFailurePaths.Count;
+                int expectedNrOfRows = assessmentSection.GetFailureMechanisms().Count() +
+                                       assessmentSection.SpecificFailurePaths.Count;
                 Assert.AreEqual(expectedNrOfRows, rows.Count);
-                AssertFailureMechanismRows(expectedDefaultSelectedAssessmentSection, rows);
-                AssertFailurePathRows(expectedDefaultSelectedAssessmentSection, rows);
+                AssertFailureMechanismRows(assessmentSection, rows);
+                AssertFailurePathRows(assessmentSection, rows);
             }
         }
 
@@ -270,10 +250,7 @@
             using (var dialog = new AssessmentSectionMergeDataProviderDialog(dialogParent))
             {
                 // When
-                AssessmentSectionMergeData result = dialog.GetMergeData(new[]
-                {
-                    TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths()
-                });
+                AssessmentSectionMergeData result = dialog.GetMergeData(TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths());
 
                 // Then
                 Assert.IsNull(result);
@@ -284,7 +261,7 @@
         public void GivenValidDialog_WhenGetMergeDataCalledAndOnlyAssessmentSectionSelectedAndImportPressed_ThenReturnsSelectedData()
         {
             // Given
-            AssessmentSection selectedAssessmentSection = TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths();
+            AssessmentSection assessmentSection = TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths();
 
             DialogBoxHandler = (formName, wnd) =>
             {
@@ -299,13 +276,10 @@
             using (var dialog = new AssessmentSectionMergeDataProviderDialog(dialogParent))
             {
                 // When
-                AssessmentSectionMergeData result = dialog.GetMergeData(new[]
-                {
-                    selectedAssessmentSection
-                });
+                AssessmentSectionMergeData result = dialog.GetMergeData(assessmentSection);
 
                 // Then
-                Assert.AreSame(selectedAssessmentSection, result.AssessmentSection);
+                Assert.AreSame(assessmentSection, result.AssessmentSection);
 
                 Assert.IsFalse(result.MergePiping);
                 Assert.IsFalse(result.MergeGrassCoverErosionInwards);
@@ -333,7 +307,7 @@
         public void GivenValidDialog_WhenGetMergeDataCalledAndAllDataSelectedAndImportPressed_ThenReturnsSelectedData()
         {
             // Given
-            AssessmentSection selectedAssessmentSection = TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths();
+            AssessmentSection assessmentSection = TestDataGenerator.GetAssessmentSectionWithAllCalculationConfigurationsAndFailurePaths();
 
             DialogBoxHandler = (formName, wnd) =>
             {
@@ -359,13 +333,10 @@
             using (var dialog = new AssessmentSectionMergeDataProviderDialog(dialogParent))
             {
                 // When
-                AssessmentSectionMergeData result = dialog.GetMergeData(new[]
-                {
-                    selectedAssessmentSection
-                });
+                AssessmentSectionMergeData result = dialog.GetMergeData(assessmentSection);
 
                 // Then
-                Assert.AreSame(selectedAssessmentSection, result.AssessmentSection);
+                Assert.AreSame(assessmentSection, result.AssessmentSection);
 
                 Assert.IsTrue(result.MergePiping);
                 Assert.IsTrue(result.MergeGrassCoverErosionInwards);
@@ -385,7 +356,7 @@
                 Assert.IsTrue(result.MergeStrengthStabilityLengthwiseConstruction);
                 Assert.IsTrue(result.MergeDuneErosion);
                 Assert.IsTrue(result.MergeTechnicalInnovation);
-                CollectionAssert.AreEqual(selectedAssessmentSection.SpecificFailurePaths, result.MergeSpecificFailurePaths);
+                CollectionAssert.AreEqual(assessmentSection.SpecificFailurePaths, result.MergeSpecificFailurePaths);
             }
         }