NullReferenceException: Object reference not set to an instance of an object

hi i get this error at the "if gas HitTest..." part of my code. Do i have to initialize something or maybe create an instance? Any help would be appreciated.

NullReferenceException: Object reference not set to an instance of an object CarMain.SendInput (.CarControl Car, Boolean reverseRequiresStop, Boolean brakeRelease) (at Assets/EdyVehiclePhysics/CarMain.js:383) CarMain.Update () (at Assets/EdyVehiclePhysics/CarMain.js:85)

 static function SendInput(Car : CarControl, reverseRequiresStop : boolean, brakeRelease : boolean) : boolean
 {
 for (var touch : Touch in Input.touches) 
         {
            if (gas.HitTest(touch.position)) // Replace GasButton with your button name
            {
                 Debug.Log("GO");
 
            }
            else if (brake.HitTest(touch.position))
            {
                 Debug.Log("STOP");
 
            }
 
            if (left.HitTest(touch.position))
            {
                 Debug.Log("LEFT");
 
            }
            else if (right.HitTest(touch.position))
            {
                 Debug.Log("RIGHT");
 
            }
         }
 }