LookAtMouse Script error

i am trying to write a script that rotates the player on the y axis but when i run the script i get this error:

NullReferenceException UnityEngine.Camera.ScreenPointToRay (Vector3 position) (at C:/BuildAgent/work/6bc5f79e0a4296d6/Runtime/ExportGenerated/Editor/Graphics.cs:674) LookAtMouse.Update () (at Assets/Standard Assets/Scripts/General Scripts/LookAtMouse.js:8)

Can someone help me with this problem?

 function Update()
 {
     var playerPlane = new Plane(Vector3.up, transform.position);
     var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
     var hitdist = 0.0;
     
     if (playerPlane.Raycast (ray, hitdist)) {
         var targetPoint = ray.GetPoint(hitdist);
         var targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
         transform.rotation = targetRotation;
     }
 }

That is the code i am using Please Help me!