diff --git a/backend/workflow_executor.py b/backend/workflow_executor.py
index 0677e05..05a6367 100644
--- a/backend/workflow_executor.py
+++ b/backend/workflow_executor.py
@@ -186,7 +186,7 @@ async def execute_workflow(
 
         return ExecutionResult(
             execution_id=execution_id,
-            workflow_id=workflow_id,
+            workflow_id=workflow_id or "N/A",  # Placeholder when graph_data is used directly
             status="completed",
             node_states=node_states,
             aggregated_result=aggregated,