for fixing test cases

Author: nishika26

backend/app/api/routes/collections.py

@@ -120,15 +120,14 @@ def create_collection(
         with_assistant=with_assistant,
     )
 
-    metadata = {}
-
+    metadata = None
     if not with_assistant:
-        metadata["assistant_note"] = (
-            "This job will create a vector store only (no Assistant). "
-            "Assistant creation happens when both 'model' and 'instructions' are included."
-        )
-
-    metadata = metadata if metadata else None
+        metadata = {
+            "note": (
+                "This job will create a vector store only (no Assistant). "
+                "Assistant creation happens when both 'model' and 'instructions' are included."
+            )
+        }
 
     return APIResponse.success_response(
         CollectionJobImmediatePublic.model_validate(collection_job), metadata=metadata