Index: Core/Gui/src/Core.Gui/Plugin/StateInfo.cs
===================================================================
diff -u -r6bce1d3c2cb767854105e8e8879ce9659c0ad9f0 -r419dd49f7777c795062212c60890eca33bc21653
--- Core/Gui/src/Core.Gui/Plugin/StateInfo.cs	(.../StateInfo.cs)	(revision 6bce1d3c2cb767854105e8e8879ce9659c0ad9f0)
+++ Core/Gui/src/Core.Gui/Plugin/StateInfo.cs	(.../StateInfo.cs)	(revision 419dd49f7777c795062212c60890eca33bc21653)
@@ -34,10 +34,11 @@
         /// </summary>
         /// <param name="symbol">The symbol of the state.</param>
         /// <param name="getRootData">The method for obtaining the root data of the state.</param>
-        public StateInfo(string symbol, Func<object, IProject> getRootData)
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="getRootData"/> is <c>null</c>.</exception>
+        public StateInfo(string symbol, Func<IProject, object> getRootData)
         {
             Symbol = symbol;
-            GetRootData = getRootData;
+            GetRootData = getRootData ?? throw new ArgumentNullException(nameof(getRootData));
         }
 
         /// <summary>
@@ -52,6 +53,6 @@
         ///     <item>out - The root data object of the state.</item>
         /// </list>
         /// </summary>
-        public Func<object, IProject> GetRootData { get; }
+        public Func<IProject, object> GetRootData { get; }
     }
 }
\ No newline at end of file
Index: Core/Gui/test/Core.Gui.Test/Plugin/StateInfoTest.cs
===================================================================
diff -u -r6bce1d3c2cb767854105e8e8879ce9659c0ad9f0 -r419dd49f7777c795062212c60890eca33bc21653
--- Core/Gui/test/Core.Gui.Test/Plugin/StateInfoTest.cs	(.../StateInfoTest.cs)	(revision 6bce1d3c2cb767854105e8e8879ce9659c0ad9f0)
+++ Core/Gui/test/Core.Gui.Test/Plugin/StateInfoTest.cs	(.../StateInfoTest.cs)	(revision 419dd49f7777c795062212c60890eca33bc21653)
@@ -19,6 +19,8 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
+using System;
+using Core.Common.Base.Data;
 using Core.Gui.Plugin;
 using NUnit.Framework;
 
@@ -32,13 +34,25 @@
         {
             // Setup
             const string symbol = "Symbol";
+            Func<IProject, object> getRootData = o => new object();
 
             // Call
-            var stateInfo = new StateInfo(symbol, null);
+            var stateInfo = new StateInfo(symbol, getRootData);
 
             // Assert
             Assert.AreEqual(symbol, stateInfo.Symbol);
-            Assert.IsNull(stateInfo.GetRootData);
+            Assert.AreSame(getRootData, stateInfo.GetRootData);
         }
+
+        [Test]
+        public void Constructor_GetRootDataNull_ThrowsArgumentNullException()
+        {
+            // Call
+            void Call() => new StateInfo(string.Empty, null);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(Call);
+            Assert.AreEqual("getRootData", exception.ParamName);
+        }
     }
 }
\ No newline at end of file