Index: Ringtoets/Integration/src/Ringtoets.Integration.Plugin/RingtoetsPlugin.cs
===================================================================
diff -u -r50b203a8d5c805fc548fb6b92c70a847190da6a5 -r2227f1d3a31b15a6d05c5385898d5da4b79dcdea
--- Ringtoets/Integration/src/Ringtoets.Integration.Plugin/RingtoetsPlugin.cs	(.../RingtoetsPlugin.cs)	(revision 50b203a8d5c805fc548fb6b92c70a847190da6a5)
+++ Ringtoets/Integration/src/Ringtoets.Integration.Plugin/RingtoetsPlugin.cs	(.../RingtoetsPlugin.cs)	(revision 2227f1d3a31b15a6d05c5385898d5da4b79dcdea)
@@ -227,7 +227,13 @@
         public override void Activate()
         {
             base.Activate();
+
+            if (Gui == null)
+            {
+                throw new InvalidOperationException("Gui cannot be null");
+            }
             assessmentSectionFromFileCommandHandler = new AssessmentSectionFromFileCommandHandler(Gui.MainWindow, Gui, Gui.DocumentViewController);
+           
         }
 
         /// <summary>