fix: Null protection on Security Descriptor owner - BED-9499

src/CommonLib/SecurityDescriptor.cs

@@ -109,7 +109,7 @@ public virtual string GetOwner(Type targetType)
         {
             // Blocking External Call -- Possible blocking through locks, and Translate call
             // see https://github.com/dotnet/runtime/blob/9d5a6a9aa463d6d10b0b0ba6d5982cc82f363dc3/src/libraries/System.Security.AccessControl/src/System/Security/AccessControl/ObjectSecurity.cs#L336
-            return _sd.GetOwner(targetType).Value;
+            return _sd.GetOwner(targetType)?.Value;
         }
     }
-}
+}

test/unit/SecurityDescriptorTests.cs

@@ -0,0 +1,21 @@
+using System.DirectoryServices;
+using System.Runtime.Versioning;
+using System.Security.Principal;
+using SharpHoundCommonLib;
+using Xunit;
+
+namespace CommonLibTest;
+
+public class SecurityDescriptorTests
+{
+    [SupportedOSPlatform("windows")]
+    [WindowsOnlyFact]
+    public void GetOwner_SecurityDescriptorWithoutOwner_ReturnsNull()
+    {
+        var descriptor = new ActiveDirectorySecurityDescriptor(new ActiveDirectorySecurity());
+
+        var owner = descriptor.GetOwner(typeof(SecurityIdentifier));
+
+        Assert.Null(owner);
+    }
+}