Fix serialization of parameters in RpcClient::get_block_production_with_config (backport #18998) (#19000)

* Fix serialization of parameters in RpcClient::get_block_production_with_config (#18998)

Params must be an array or null.

(cherry picked from commit 58f395257b)

# Conflicts:
#	client/src/mock_sender.rs

* Fix conflict

Co-authored-by: Brian Anderson <andersrb@gmail.com>
Co-authored-by: Tyera Eulberg <tyera@solana.com>

client/src/mock_sender.rs

@@ -2,7 +2,10 @@ use {
     crate::{
         client_error::Result,
         rpc_request::RpcRequest,
-        rpc_response::{Response, RpcResponseContext, RpcVersionInfo},
+        rpc_response::{
+            Response, RpcBlockProduction, RpcBlockProductionRange, RpcResponseContext,
+            RpcVersionInfo,
+        },
         rpc_sender::RpcSender,
     },
     serde_json::{json, Number, Value},
@@ -148,6 +151,19 @@ impl RpcSender for MockSender {
                     feature_set: Some(version.feature_set),
                 })
             }
+            "getBlockProduction" => {
+                let map = vec![(PUBKEY.to_string(), (1, 1))].into_iter().collect();
+                json!(Response {
+                    context: RpcResponseContext { slot: 1 },
+                    value: RpcBlockProduction {
+                        by_identity: map,
+                        range: RpcBlockProductionRange {
+                            first_slot: 0,
+                            last_slot: 0,
+                        },
+                    },
+                })
+            }
             _ => Value::Null,
         };
         Ok(val)

client/src/rpc_client.rs

@@ -482,7 +482,7 @@ impl RpcClient {
         &self,
         config: RpcBlockProductionConfig,
     ) -> RpcResult<RpcBlockProduction> {
-        self.send(RpcRequest::GetBlockProduction, json!(config))
+        self.send(RpcRequest::GetBlockProduction, json!([config]))
     }
 
     pub fn get_stake_activation(
@@ -2245,4 +2245,23 @@ mod tests {
         let rpc_client = RpcClient::new_mock("succeeds".to_string());
         thread::spawn(move || rpc_client);
     }
+
+    // Regression test that the get_block_production_with_config
+    // method internally creates the json params array correctly.
+    #[test]
+    fn get_block_production_with_config_no_error() -> ClientResult<()> {
+        let rpc_client = RpcClient::new_mock("succeeds".to_string());
+
+        let config = RpcBlockProductionConfig {
+            identity: None,
+            range: None,
+            commitment: None,
+        };
+
+        let prod = rpc_client.get_block_production_with_config(config)?.value;
+
+        assert!(!prod.by_identity.is_empty());
+
+        Ok(())
+    }
 }