fix(providers): don't default to "latest" block ID for `eth_estimateGas` (#1657)

* Don't default to 'latest' block ID for eth_estimateGas

* Add changelog entry

* Amend comment

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Unreleased
 
+- Stop defaulting to the `"latest"` block in `eth_estimateGas` params [#1657](https://github.com/gakonst/ethers-rs/pull/1657)
 - Fix geth trace types for debug_traceTransaction rpc
 - Fix RLP decoding of legacy `Transaction`
 - Fix RLP encoding of `TransactionReceipt` [#1661](https://github.com/gakonst/ethers-rs/pull/1661)

ethers-providers/src/provider.rs

@@ -574,8 +574,14 @@ impl<P: JsonRpcClient> Middleware for Provider<P> {
         block: Option<BlockId>,
     ) -> Result<U256, ProviderError> {
         let tx = utils::serialize(tx);
-        let block = utils::serialize(&block.unwrap_or_else(|| BlockNumber::Latest.into()));
-        self.request("eth_estimateGas", [tx, block]).await
+        // Some nodes (e.g. old Optimism clients) don't support a block ID being passed as a param,
+        // so refrain from defaulting to BlockNumber::Latest.
+        let params = if let Some(block_id) = block {
+            vec![tx, utils::serialize(&block_id)]
+        } else {
+            vec![tx]
+        };
+        self.request("eth_estimateGas", params).await
     }
 
     async fn create_access_list(