Index: Ringtoets/Common/src/Ringtoets.Common.IO/ReferenceLines/ReferenceLineImporter.cs
===================================================================
diff -u -r75b7759b5721edc5e0458229e2d727723f527391 -r9fe132b5fdbde6b462235fccc39bccd521093a4f
--- Ringtoets/Common/src/Ringtoets.Common.IO/ReferenceLines/ReferenceLineImporter.cs	(.../ReferenceLineImporter.cs)	(revision 75b7759b5721edc5e0458229e2d727723f527391)
+++ Ringtoets/Common/src/Ringtoets.Common.IO/ReferenceLines/ReferenceLineImporter.cs	(.../ReferenceLineImporter.cs)	(revision 9fe132b5fdbde6b462235fccc39bccd521093a4f)
@@ -45,13 +45,17 @@
         /// <param name="updateHandler">The object responsible for updating the
         /// <see cref="ReferenceLine"/>.</param>
         /// <param name="filePath">The path to the file to import from.</param>
-        /// <exception cref="ArgumentNullException">Thrown when <paramref name="importTarget"/>
-        /// or <paramref name="filePath"/> is <c>null</c>.</exception>
+        /// <exception cref="ArgumentNullException">Thrown when any parameter is <c>null</c>.</exception>
         public ReferenceLineImporter(ReferenceLine importTarget,
                                      IReferenceLineUpdateHandler updateHandler,
                                      string filePath)
             : base(filePath, importTarget)
         {
+            if (updateHandler == null)
+            {
+                throw new ArgumentNullException(nameof(updateHandler));
+            }
+
             this.updateHandler = updateHandler;
         }