fix: use None instead of empty tuple

Co-authored-by: antazoey <jules@apeworx.io>

src/ape_ethereum/provider.py

@@ -290,7 +290,7 @@ def estimate_gas_cost(self, txn: TransactionAPI, block_id: Optional[BlockID] = N
             except Exception:
                 call_trace = None
 
-            traces = tuple()
+            traces = None
             tb = None
             if call_trace and txn_params.get("to"):
                 traces = (self._create_trace_frame(t) for t in call_trace[1])