message: Request identifier can be optional
diff: @@ -39,7 +39,8 @@ pub struct TxnAuthrAgrmtAcceptanceData {
  #[serde(rename_all = "camelCase")]
  pub struct Request<T: serde::Serialize> {
  pub req_id: u64,
  - pub identifier: String,
  + #[serde(skip_serializing_if = "Option::is_none")]
  + pub identifier: Option<String>,
  pub operation: T,
  pub protocol_version: Option<usize>,
  #[serde(skip_serializing_if = "Option::is_none")]
  @@ -56,7 +57,7 @@ impl<T: serde::Serialize> Request<T> {
  pub fn new(req_id: u64, identifier: &str, operation: T, protocol_version: usize) -> Request<T> {
  Request {
  req_id,
  - identifier: identifier.to_string(),
  + identifier: Some(identifier.to_string()),
  operation,
  protocol_version: Some(protocol_version),
  signature: None,
  