fix:edge case for no agent address

app.py

@@ -56,12 +56,16 @@ def fetch_and_aggregate_transactions():
     for chain_name, service_registry in service_registries.items():
         web3 = web3_instances[chain_name]
         total_services = service_registry.functions.totalSupply().call()
+
         for service_id in range(1, total_services + 1):
             service = service_registry.functions.getService(service_id).call()
             agent_ids = service[-1]
-
             if 40 in agent_ids or 25 in agent_ids:
-                agent_address = service_registry.functions.getAgentInstances(service_id).call()[1][0]
+                agent_instances = service_registry.functions.getAgentInstances(service_id).call()[1][0]
+                if not agent_instances:
+                    print(f"No agent address found for service ID: {service_id}")
+                    continue 
+                agent_address = agent_instances[0]
                 response_transfers = get_transfers("valory", agent_address)
                 transfers = response_transfers.get("transfers", [])