message: Fixed state proof checking for DELTA
diff: @@ -585,7 +585,11 @@ fn _parse_reply_for_proof_value(json_msg: &SJsonValue, data: Option<&str>, parse
  };
  }
  constants::GET_REVOC_REG_DELTA => {
  - value["val"] = parsed_data["value"]["accum_to"].clone();
  + if !parsed_data["value"]["accum_to"].is_null() {
  + value["val"] = parsed_data["value"]["accum_to"].clone()
  + } else {
  + return Ok(None)
  + }
  }
  constants::GET_TXN_AUTHR_AGRMT => {
  if _is_full_taa_state_value_expected(sp_key) {
  