guarantee round-trip

chain/types/ethtypes/eth_transactions.go

@@ -111,6 +111,10 @@ func EthTxArgsFromMessage(msg *types.Message) (EthTxArgs, error) {
 			if paramsReader.Len() != 0 {
 				return EthTxArgs{}, xerrors.Errorf("extra data found in params")
 			}
+			if len(params) == 0 {
+				// Otherwise, we don't get a guaranteed round-trip.
+				return EthTxArgs{}, xerrors.Errorf("cannot invoke contracts with empty parameters from an eth-account")
+			}
 		}
 	}