diff --git a/SabreTools.IO.Test/Extensions/XmlTextWriterExtensionsTests.cs b/SabreTools.IO.Test/Extensions/XmlTextWriterExtensionsTests.cs
new file mode 100644
index 0000000..6961c1f
--- /dev/null
+++ b/SabreTools.IO.Test/Extensions/XmlTextWriterExtensionsTests.cs
@@ -0,0 +1,242 @@
+using System;
+using System.IO;
+using System.Text;
+using System.Xml;
+using SabreTools.IO.Extensions;
+using Xunit;
+
+namespace SabreTools.IO.Test.Extensions
+{
+    public class XmlTextWriterExtensionsTests
+    {
+        [Fact]
+        public void WriteRequiredAttributeString_NullInputThrow_Throws()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element />";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteStartElement("element");
+            Assert.Throws<ArgumentNullException>(()
+                => writer.WriteRequiredAttributeString("attr", null, throwOnError: true));
+            writer.WriteEndElement();
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(52, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteRequiredAttributeString_NullInputNoThrow_Writes()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element attr=\"\" />";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteStartElement("element");
+            writer.WriteRequiredAttributeString("attr", null, throwOnError: false);
+            writer.WriteEndElement();
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(60, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteRequiredAttributeString_ValidInput_Writes()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element attr=\"val\" />";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteStartElement("element");
+            writer.WriteRequiredAttributeString("attr", "val", throwOnError: false);
+            writer.WriteEndElement();
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(63, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteRequiredElementString_NullInputThrow_Throws()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?>";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            Assert.Throws<ArgumentNullException>(()
+                => writer.WriteRequiredElementString("element", null, throwOnError: true));
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(41, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteRequiredElementString_NullInputNoThrow_Writes()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element></element>";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteRequiredElementString("element", null, throwOnError: false);
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(60, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteRequiredElementString_ValidInput_Writes()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element>val</element>";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteRequiredElementString("element", "val", throwOnError: false);
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(63, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+    
+        [Fact]
+        public void WriteOptionalAttributeString_NullInput_NoWrite()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element />";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteStartElement("element");
+            writer.WriteOptionalAttributeString("attr", null);
+            writer.WriteEndElement();
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(52, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteOptionalAttributeString_EmptyInput_NoWrite()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element />";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteStartElement("element");
+            writer.WriteOptionalAttributeString("attr", string.Empty);
+            writer.WriteEndElement();
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(52, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteOptionalAttributeString_ValidInput_Writes()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element attr=\"val\" />";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteStartElement("element");
+            writer.WriteOptionalAttributeString("attr", "val");
+            writer.WriteEndElement();
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(63, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+    
+        [Fact]
+        public void WriteOptionalElementString_NullInput_NoWrite()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?>";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteOptionalElementString("element", null);
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(41, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteOptionalElementString_EmptyInput_NoWrite()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?>";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteOptionalElementString("element", string.Empty);
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(41, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+
+        [Fact]
+        public void WriteOptionalElementString_ValidInput_Writes()
+        {
+            string expected = "<?xml version=\"1.0\" encoding=\"utf-8\"?><element>val</element>";
+
+            var stream = new MemoryStream();
+            var writer = new XmlTextWriter(stream, Encoding.UTF8);
+
+            writer.WriteStartDocument();
+            writer.WriteOptionalElementString("element", "val");
+            writer.Flush();
+
+            // Length includes UTF-8 BOM
+            Assert.Equal(63, stream.Length);
+            string actual = Encoding.UTF8.GetString(stream.ToArray(), 3, (int)stream.Length - 3);
+            Assert.Equal(expected, actual);
+        }
+    }
+}
\ No newline at end of file
diff --git a/SabreTools.IO/Extensions/XmlTextWriterExtensions.cs b/SabreTools.IO/Extensions/XmlTextWriterExtensions.cs
index 9f384f0..13d8b15 100644
--- a/SabreTools.IO/Extensions/XmlTextWriterExtensions.cs
+++ b/SabreTools.IO/Extensions/XmlTextWriterExtensions.cs
@@ -15,7 +15,7 @@ namespace SabreTools.IO.Extensions
         /// <param name="localName">Name of the element</param>
         /// <param name="value">Value to write in the element</param>
         /// <param name="throwOnError">Indicates if an error should be thrown on a missing required value</param>
-        public static void WriteRequiredAttributeString(this XmlTextWriter writer, string localName, string value, bool throwOnError = false)
+        public static void WriteRequiredAttributeString(this XmlTextWriter writer, string localName, string? value, bool throwOnError = false)
         {
             // Throw an exception if we are configured to
             if (value == null && throwOnError)
@@ -31,7 +31,7 @@ namespace SabreTools.IO.Extensions
         /// <param name="localName">Name of the element</param>
         /// <param name="value">Value to write in the element</param>
         /// <param name="throwOnError">Indicates if an error should be thrown on a missing required value</param>
-        public static void WriteRequiredElementString(this XmlTextWriter writer, string localName, string value, bool throwOnError = false)
+        public static void WriteRequiredElementString(this XmlTextWriter writer, string localName, string? value, bool throwOnError = false)
         {
             // Throw an exception if we are configured to
             if (value == null && throwOnError)
@@ -51,7 +51,7 @@ namespace SabreTools.IO.Extensions
         /// <param name="writer">XmlTextWriter to write out with</param>
         /// <param name="localName">Name of the attribute</param>
         /// <param name="value">Value to write in the attribute</param>
-        public static void WriteOptionalAttributeString(this XmlTextWriter writer, string localName, string value)
+        public static void WriteOptionalAttributeString(this XmlTextWriter writer, string localName, string? value)
         {
             if (!string.IsNullOrEmpty(value))
                 writer.WriteAttributeString(localName, value);
@@ -63,7 +63,7 @@ namespace SabreTools.IO.Extensions
         /// <param name="writer">XmlTextWriter to write out with</param>
         /// <param name="localName">Name of the element</param>
         /// <param name="value">Value to write in the element</param>
-        public static void WriteOptionalElementString(this XmlTextWriter writer, string localName, string value)
+        public static void WriteOptionalElementString(this XmlTextWriter writer, string localName, string? value)
         {
             if (!string.IsNullOrEmpty(value))
                 writer.WriteElementString(localName, value);