diff --git a/backend/src/services/schedule/service.py b/backend/src/services/schedule/service.py
index f0ec7c4..e34a2d1 100644
--- a/backend/src/services/schedule/service.py
+++ b/backend/src/services/schedule/service.py
@@ -332,7 +332,7 @@ def _build_generation_response(
         scheduling_dataset,
         conflicts_response: dict,
         parameters: dict,
-        merges: dict[str, list[str]],
+        merges: dict[str, list[str]] = None,
     ) -> dict[str, Any]:
         """Build response for generate_schedule endpoint."""
         # Count unique students