diff --git a/src/C++/Driver/src/main.cpp b/src/C++/Driver/src/main.cpp
index e9ac6b4..5e3ebdc 100644
--- a/src/C++/Driver/src/main.cpp
+++ b/src/C++/Driver/src/main.cpp
@@ -44,18 +44,18 @@ std::string readMQTT()
 void parseMQTT(std::string message){
     if(message == "up"){
         robot.forward(600);
-        message = NULL;
+        message = 'null';
     }
     else if(message == "left"){
         robot.Rotate(90);
-        message = NULL;
+        message = 'null';
 
     }
     else if(message == "down"){
         robot.Rotate(-90);
-        message = NULL;
+        message = 'null';
     }
-    else if(message = NULL){
+    else if(message = 'null'){
         robot.sendNullMessage();
     }
     else{