diff --git a/csharp/Pehape/Pehape.csproj b/csharp/Pehape/Pehape.csproj
index aa23382..ff342aa 100644
--- a/csharp/Pehape/Pehape.csproj
+++ b/csharp/Pehape/Pehape.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net9.0</TargetFramework>
     <Nullable>enable</Nullable>
     <EnforceCodeStyleInBuild>False</EnforceCodeStyleInBuild>
     <AnalysisLevel>latest-all</AnalysisLevel>
diff --git a/csharp/Pehape/String/Explode.cs b/csharp/Pehape/String/Explode.cs
index da7a46f..d1fc805 100644
--- a/csharp/Pehape/String/Explode.cs
+++ b/csharp/Pehape/String/Explode.cs
@@ -16,7 +16,7 @@ public static partial class PHP {
 		/// <returns>An array of strings.</returns>
 		public static string[] Explode(string? separator, string str, int? limit = null) {
 			if (separator is "") throw new ArgumentException("Separator cannot be empty.", nameof(separator));
-			if (str is null) throw new ArgumentNullException(nameof(str));
+			ArgumentNullException.ThrowIfNull(str);
 			return limit switch {
 				null => str.Split(separator),
 				> 0 => str.Split(separator).Take(limit.Value).ToArray(),
@@ -37,7 +37,7 @@ public static string[] Explode(string? separator, string str, int? limit = null)
 		/// one element is returned.</param>
 		/// <returns>An array of strings.</returns>
 		public static string[] Explode(char separator, string str, int? limit = null) {
-			if (str is null) throw new ArgumentNullException(nameof(str));
+			ArgumentNullException.ThrowIfNull(str);
 			return limit switch {
 				null => str.Split(separator),
 				> 0 => str.Split(separator).Take(limit.Value).ToArray(),
diff --git a/csharp/Pehape/String/Levenshtein.cs b/csharp/Pehape/String/Levenshtein.cs
index 1907ce2..68f33d6 100644
--- a/csharp/Pehape/String/Levenshtein.cs
+++ b/csharp/Pehape/String/Levenshtein.cs
@@ -16,8 +16,8 @@ public static partial class PHP {
 		public static int Levenshtein(string string1, string string2, int insertCost = 1, int replaceCost = 1, int deleteCost = 1) {
 			// Ported from https://github.com/php/php-src/blob/master/ext/standard/levenshtein.c
 
-			if (string1 is null) throw new ArgumentNullException(nameof(string1));
-			if (string2 is null) throw new ArgumentNullException(nameof(string2));
+			ArgumentNullException.ThrowIfNull(string1);
+			ArgumentNullException.ThrowIfNull(string2);
 			if (insertCost < 0) throw new ArgumentException("InsertCost cannot be negative.", nameof(insertCost));
 			if (replaceCost < 0) throw new ArgumentException("ReplaceCost cannot be negative.", nameof(replaceCost));
 			if (deleteCost < 0) throw new ArgumentException("DeleteCost cannot be negative.", nameof(deleteCost));
@@ -28,7 +28,7 @@ public static int Levenshtein(string string1, string string2, int insertCost = 1
 
 			Span<int> p1 = stackalloc int[string2.Length + 1];
 			Span<int> p2 = stackalloc int[string2.Length + 1];
-			bool swap = false;
+			var swap = false;
 
 			for (var i2 = 0; i2 <= string2.Length; i2++) {
 				p1[i2] = i2 * insertCost;
@@ -42,7 +42,7 @@ public static int Levenshtein(string string1, string string2, int insertCost = 1
 					if (c1 < c0) {
 						c0 = c1;
 					}
-					int c2 = (swap ? p1 : p2)[i2] + insertCost;
+					var c2 = (swap ? p1 : p2)[i2] + insertCost;
 					if (c2 < c0) {
 						c0 = c2;
 					}
diff --git a/csharp/Pehape/String/StrRot13.cs b/csharp/Pehape/String/StrRot13.cs
index b2f0fcd..44f3f56 100644
--- a/csharp/Pehape/String/StrRot13.cs
+++ b/csharp/Pehape/String/StrRot13.cs
@@ -14,10 +14,10 @@ public static partial class PHP {
 		/// <param name="str">The input string.</param>
 		/// <returns>Returns the ROT13 version of the given string.</returns>
 		public static string StrRot13(string str) {
-			if (str is null) throw new ArgumentNullException(nameof(str));
+			ArgumentNullException.ThrowIfNull(str);
 
 			var buffer = new StringBuilder();
-			foreach (char ch in str) {
+			foreach (var ch in str) {
 				buffer.Append((char)(ch switch {
 					>= 'a' and <= 'z' => ch > 'm' ? ch - 13 : ch + 13,
 					>= 'A' and <= 'Z' => ch > 'M' ? ch - 13 : ch + 13,