Update backend_utils.py

backend_utils.py

@@ -470,7 +470,7 @@ def make_predictions(input_query,
     library_ids, library_names = retrieve_libraries(model_retrieval, input_query, db_metadata)
 
     if len(library_ids) == 0:
-        return {'status': 999}
+        return "null"
 
     print("generate usage patterns")
     predictions = generate_api_usage_patterns_batch(