diff --git a/src/Sage.Engine.Tests/Functions/StringTests.cs b/src/Sage.Engine.Tests/Functions/StringTests.cs
index 45e6e94..422a1d2 100644
--- a/src/Sage.Engine.Tests/Functions/StringTests.cs
+++ b/src/Sage.Engine.Tests/Functions/StringTests.cs
@@ -12,7 +12,7 @@ internal class StringTests : FunctionTestBase
         [TestCase("Hello World", "Hello ", null, "World")]
         [TestCase("Hello 1World", "Hello ", 1, "World")]
         [TestCase("1World", null, 1, "World")]
-        public void TestConcat(string expected, params object[] arguments)
+        public void TestConcat(string expected, params object?[] arguments)
         {
             string actual = this._runtimeContext.CONCAT(arguments);
             Assert.That(actual, Is.EqualTo(expected));
@@ -25,7 +25,7 @@ public void TestConcat(string expected, params object[] arguments)
         [TestCase(null, "o", 0)]
         [TestCase(null, null, 0)]
         [TestCase("Hello", null, 0)]
-        public void TestIndexOf(string subject, string search, int expected)
+        public void TestIndexOf(string? subject, string? search, int expected)
         {
             int actual = this._runtimeContext.INDEXOF(subject, search);
             Assert.That(actual, Is.EqualTo(expected));
diff --git a/src/Sage.Engine.Tests/Functions/UtilityTests.cs b/src/Sage.Engine.Tests/Functions/UtilityTests.cs
index e14aab1..09d6d84 100644
--- a/src/Sage.Engine.Tests/Functions/UtilityTests.cs
+++ b/src/Sage.Engine.Tests/Functions/UtilityTests.cs
@@ -13,7 +13,7 @@ internal class UtilityTests : FunctionTestBase
         [TestCase("Hello", "Hello")]
         [TestCase(1, "1")]
         [TestCase(true, "True")]
-        public void TestOutputAndV(object data, string expected)
+        public void TestOutputAndV(object? data, string expected)
         {
             this._runtimeContext.OUTPUT(data);
             Assert.That(this._runtimeContext.PopContext(), Is.EqualTo(expected));
@@ -24,7 +24,7 @@ public void TestOutputAndV(object data, string expected)
         [TestCase("Hello", "Hello")]
         [TestCase(1, "1")]
         [TestCase(true, "True")]
-        public void TestOutputLine(object data, string expected)
+        public void TestOutputLine(object? data, string expected)
         {
             this._runtimeContext.OUTPUTLINE(data);
 
@@ -36,7 +36,7 @@ public void TestOutputLine(object data, string expected)
         [TestCase("Hello", "Hello")]
         [TestCase(1, "1")]
         [TestCase(true, "True")]
-        public void TestV(object data, string expected)
+        public void TestV(object? data, string expected)
         {
             string result = this._runtimeContext.V(data);
             Assert.That(result, Is.EqualTo(expected));
diff --git a/src/Sage.Engine/Runtime/Functions/String.cs b/src/Sage.Engine/Runtime/Functions/String.cs
index 4b7251e..da4b6d3 100644
--- a/src/Sage.Engine/Runtime/Functions/String.cs
+++ b/src/Sage.Engine/Runtime/Functions/String.cs
@@ -44,7 +44,7 @@ public string CONCAT(params object[] strings)
         /// <param name="subject">The string to search</param>
         /// <param name="search">The string to find</param>
         /// <returns>The position that search exists in subject. If not found, -1 is returned.</returns>
-        public int INDEXOF(object subject, object search)
+        public int INDEXOF(object? subject, object? search)
         {
             if (subject == null || search == null)
             {
diff --git a/src/Sage.Engine/Runtime/Functions/Utility.cs b/src/Sage.Engine/Runtime/Functions/Utility.cs
index d568a31..9b9578b 100644
--- a/src/Sage.Engine/Runtime/Functions/Utility.cs
+++ b/src/Sage.Engine/Runtime/Functions/Utility.cs
@@ -97,7 +97,7 @@ public bool ISNULL(object expression)
         /// Outputs to where this block appears in the content.
         /// </summary>
         /// <param name="data">The data to add to the output stream</param>
-        public void OUTPUT(object data)
+        public void OUTPUT(object? data)
         {
             Output(data);
         }
@@ -106,7 +106,7 @@ public void OUTPUT(object data)
         /// Outputs to where this block appears in the content, with a newline
         /// </summary>
         /// <param name="data">The data to add to the output stream</param>
-        public void OUTPUTLINE(object data)
+        public void OUTPUTLINE(object? data)
         {
             OutputLine(data);
         }