fix: only run tracing example if env var is set (#1517)

examples/geth_trace_transaction.rs

@@ -1,16 +1,19 @@
 use ethers::prelude::*;
 use eyre::Result;
-use std::{env, str::FromStr};
+use std::str::FromStr;
 
+/// use `debug_traceTransaction` to fetch traces
+/// requires, a valid endpoint in `RPC_URL` env var that supports `debug_traceTransaction`
 #[tokio::main]
 async fn main() -> Result<()> {
-    let rpc_url: String = env::var("RPC_URL")?;
-    let client = Provider::<Http>::try_from(rpc_url)?;
+    if let Ok(url) = std::env::var("RPC_URL") {
+        let client = Provider::<Http>::try_from(url)?;
         let tx_hash = "0x97a02abf405d36939e5b232a5d4ef5206980c5a6661845436058f30600c52df7";
         let h: H256 = H256::from_str(tx_hash)?;
         let options: GethDebugTracingOptions = GethDebugTracingOptions::default();
         let traces = client.debug_trace_transaction(h, options).await?;
         println!("{:?}", traces);
+    }
 
     Ok(())
 }