Simple Script getting Errors.

Hello there :) I'm getting an error on the simplest of scripts that I cannot seem to fix :(

Here is the script :

 private var ray : Ray;
     private var rayCastHit : RaycastHit;
     
     function Update()
     {
         if(Input.GetMouseButton(0))
         {
            ray = Camera.main.ScreenPointToRay (Input.mousePostion);
             
             if (Physics.Raycast (ray, rayCastHit))
             {
                 transform.position.x = rayCastHit.point.x;
                 
             }
             
         }
     }

I am getting this error :

NullReferenceException: Object reference not set to an instance of an object Paddle.Update () (at Assets/PongScripts/Paddle.js:8)

If anyone can tell me how to fix this that would be awesome ! :D