diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index 286329b6ec..c347ca84f3 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -37,9 +37,13 @@ public sealed class SwitchBuilder
 
         HashSet<int> indicies = [];
 
-        foreach (ExecutorBinding executor in executors)
+        int executorIndex = 0;
+        foreach (ExecutorBinding? executor in executors)
         {
-            Throw.IfNull(executor, nameof(executors));
+            if (executor is null)
+            {
+                throw new ArgumentNullException(nameof(executors), $"Executors collection contains a null element at index {executorIndex}.");
+            }
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -49,6 +53,7 @@ public sealed class SwitchBuilder
             }
 
             indicies.Add(index);
+            executorIndex++;
         }
 
         Func<object?, bool> casePredicate = WorkflowBuilder.CreateConditionFunc(predicate)!;
@@ -66,9 +71,13 @@ public sealed class SwitchBuilder
     {
         Throw.IfNull(executors);
 
-        foreach (ExecutorBinding executor in executors)
+        int executorIndex = 0;
+        foreach (ExecutorBinding? executor in executors)
         {
-            Throw.IfNull(executor, nameof(executors));
+            if (executor is null)
+            {
+                throw new ArgumentNullException(nameof(executors), $"Executors collection contains a null element at index {executorIndex}.");
+            }
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -78,6 +87,7 @@ public sealed class SwitchBuilder
             }
 
             this._defaultIndicies.Add(index);
+            executorIndex++;
         }
 
         return this;
diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index 179dc78c88..c261036c6b 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -128,14 +128,16 @@ public static class WorkflowBuilderExtensions
         Throw.IfNull(targets);
 
         List<ExecutorBinding> targetList = [];
+        int targetIndex = 0;
         foreach (ExecutorBinding? target in targets)
         {
             if (target is null)
             {
-                throw new ArgumentNullException(nameof(targets), "Targets collection cannot contain null elements.");
+                throw new ArgumentNullException(nameof(targets), $"Targets collection contains a null element at index {targetIndex}.");
             }
 
             targetList.Add(target);
+            targetIndex++;
         }
 
         Throw.IfNullOrEmpty(targetList, nameof(targets));