Refactor code to handle response_transfers with missing "transfers" key

app.py

@@ -94,7 +94,9 @@ def fetch_and_aggregate_transactions():
         if 25 in agent_ids:
             agent_address = service_registry.functions.getAgentInstances(service_id).call()[1][0]
             response_transfers = get_transfers("valory", agent_address)
-            aggregated_transactions.extend(response_transfers["transfers"])
+            transfers = response_transfers.get("transfers", [])
+            if isinstance(transfers, list):
+                aggregated_transactions.extend(transfers)
         
             # Track the daily number of agents
             creation_event = service_registry.events.CreateService.create_filter(