Added null input handling to reverse.

The reverse function previously didn't handle null values gracefully and would just throw null reference exceptions. By throwing an ArgumentNullException instead, the function will now alert consumers directly to the null input instead of misleading them.

src/Hussy.Net/Display/Reverse.cs

@@ -33,7 +33,10 @@ public static partial class Hussy
     /// </returns>
     public static string Rev<T>(T input)
     {
-        var stringValue = input.ToString();
+        var stringValue = input?.ToString();
+        if (stringValue is null)
+            throw new ArgumentNullException(nameof(input), message: "Unable to reverse a null input.");
+
         var reversedSequence = stringValue.Reverse().ToArray();
         return new string(reversedSequence);
     }

test/Hussy.Net.Tests/Display/ReverseTests.cs

@@ -14,6 +14,8 @@ You may obtain a copy of the License at
    limitations under the License.
 */
 
+using System.Security.Cryptography;
+
 namespace Hussy.Net.Tests.Display;
 
 public class ReverseTests
@@ -27,4 +29,16 @@ public void Reverse_ValidInput_ReversesInput()
         const string expectation = "cba";
         Assert.Equal(expectation, reversal);
     }
+
+    [Fact]
+    public void Reverse_NullInput_ThrowsArgumentNullException()
+    {
+        Assert.Throws<ArgumentNullException>(TestInvocation);
+
+        static void TestInvocation()
+        {
+            const string? testValue = null;
+            _ = Rev(testValue!);
+        }
+    }
 }