diff --git a/README.md b/README.md
index 66884879..dba61df0 100644
--- a/README.md
+++ b/README.md
@@ -145,7 +145,7 @@ cmake --build . --target <example-name>
 [Python](binding/python/example)
 * Python API is nearly identical to C++ API and covers nearly all the functionalities from C++ API.
 * Build and install the Python binding as shown [above](#python).
-* Run python3 main.py.
+* Run `python3 main.py`.
 
 ## Documentations
 
diff --git a/include/ccapi_cpp/ccapi_ws_connection.h b/include/ccapi_cpp/ccapi_ws_connection.h
index a7a550e6..9ca11bbf 100644
--- a/include/ccapi_cpp/ccapi_ws_connection.h
+++ b/include/ccapi_cpp/ccapi_ws_connection.h
@@ -91,7 +91,7 @@ class WsConnection CCAPI_FINAL {
       : url(url), group(group), subscriptionList(subscriptionList), credential(credential), streamPtr(streamPtr) {
     this->id = this->url + "||" + this->group + "||" + ccapi::toString(this->subscriptionList) + "||" + ccapi::toString(this->credential);
     this->correlationIdList.reserve(subscriptionList.size());
-    std::transform(subscriptionList.cbegin(), subscriptionList.cend(), this->correlationIdList.begin(),
+    std::transform(subscriptionList.cbegin(), subscriptionList.cend(), std::back_inserter(this->correlationIdList),
                    [](Subscription subscription) { return subscription.getCorrelationId(); });
     this->setUrlParts();
   }
diff --git a/include/ccapi_cpp/service/ccapi_market_data_service.h b/include/ccapi_cpp/service/ccapi_market_data_service.h
index cfefae6b..9b8c4677 100644
--- a/include/ccapi_cpp/service/ccapi_market_data_service.h
+++ b/include/ccapi_cpp/service/ccapi_market_data_service.h
@@ -136,7 +136,7 @@ class MarketDataService : public Service {
               CCAPI_LOGGER_TRACE("fail");
               std::vector<std::string> correlationIdList;
               correlationIdList.reserve(subscriptionListGivenInstrumentGroup.size());
-              std::transform(subscriptionListGivenInstrumentGroup.cbegin(), subscriptionListGivenInstrumentGroup.cend(), correlationIdList.begin(),
+              std::transform(subscriptionListGivenInstrumentGroup.cbegin(), subscriptionListGivenInstrumentGroup.cend(), std::back_inserter(correlationIdList),
                              [](Subscription subscription) { return subscription.getCorrelationId(); });
               that->onError(Event::Type::SUBSCRIPTION_STATUS, Message::Type::SUBSCRIPTION_FAILURE, ec, "create stream", correlationIdList);
               return;
diff --git a/test/test_unit/src/common/util/ccapi_util_test.cpp b/test/test_unit/src/common/util/ccapi_util_test.cpp
index b4315d5e..47e8b334 100644
--- a/test/test_unit/src/common/util/ccapi_util_test.cpp
+++ b/test/test_unit/src/common/util/ccapi_util_test.cpp
@@ -112,6 +112,14 @@ TEST(UtilStringTest, normalizeDecimalString_5) {
   EXPECT_EQ(UtilString::normalizeDecimalString(original), "1.1");
   EXPECT_EQ(UtilString::normalizeDecimalString(original.c_str()), "1.1");
 }
+TEST(UtilStringTest, toUpper) {
+  std::string original("ab");
+  EXPECT_EQ(UtilString::toUpper(original), "AB");
+}
+TEST(UtilStringTest, toLower) {
+  std::string original("AB");
+  EXPECT_EQ(UtilString::toLower(original), "ab");
+}
 TEST(UtilTimeTest, divideSecondsStr_1) {
   std::string str("1634929946");
   EXPECT_EQ(UtilTime::divide(str), (std::make_pair<long long, long long>(1634929946, 0)));