Unity - why getcomponent for script returns null when script is attached to game object in scene

Question

I've created a TileMap. My enemy is a simple cylinder with an "EnemyMover.cs" script attached and is in the scene (hierarchy) before play is pressed. (Not instantiated during runtime)

On a separate object, I have a "TargetLocator" script which attempts to utilize GetComponent to find the cylinder script component when instantiated by click on a tile on the map during runtime.

    public class TargetLocator : MonoBehaviour
{
    [SerializeField] private Transform weapon;
    private Transform target;
    
    void Start()
    {
        target = GetComponent<EnemyMover>().transform;
    }
    
    void Update()
    {
        AimWeapon();
    }

    void AimWeapon()
    {
        weapon.LookAt(target);
    }
}

The error:

NullReferenceException: Object reference not set to an instance of an object TargetLocator.Start () (at Assets/Towers/TargetLocator.cs:12)

I should mention that I've attempted to:

1. Reset Unity
2. remove the transform and verify only the object
3. Add a rigidbody to the enemy (cylinder)
4. Add a collider

All still return null except rigidbody but that causes the item to fall through the floor and still doesn't target the enemy.

    public class EnemyMover : MonoBehaviour
    {
        [SerializeField] private List<Waypoint> path = new List<Waypoint>();
        [SerializeField] [Range(0f, 5f)] private float speed = 1f;
    
        void Start()
        {
            StartCoroutine(FollowPath());
        }
    
        IEnumerator FollowPath()
        {
            foreach (Waypoint waypoint in path)
            {
                Vector3 startPos = transform.position;
                Vector3 endPos = waypoint.transform.position;
                float travelPercent = 0f;
                
                // todo reintroduce when object can face
                // transform.LookAt(endPos);
    
                while (travelPercent < 1f)
                {
                    travelPercent += Time.deltaTime * speed;
                    transform.position = Vector3.Lerp(startPos, endPos, travelPercent);
                    yield return new WaitForEndOfFrame();
                }
            }
        }
    }

Answer 1

Rather than transform , which is the real-world location of a object, try calling a method that is in that script. E.G EnemyMover

 public class EnemyMover: MonoBehaviour
{
    private Transform target;
    
    public Transform CalculateTarget()
    {
        target = GetComponent<Player>().transform;
        return target;
    }
}

Then in TargetLocator you would call:

target = GetComponent<EnemyMover>().CalculateTarget();

Answer 2

It doesn't look like the TargetLocator is attached to the same GameObject as the EnemyMover.

You say yourself

On a separate object, I have a "TargetLocator" script which attempts to utilize GetComponent to find the cylinder script component when instantiated by click on a tile on the map during runtime.

Component.GetComponent looks for a component on the given Component (MonoBehaviour inherits from it) instance. In your case this -> the reference of the TargetLocator itself.

You would rather want to use e.g. FindObjectOfType which looks for the component of given type on any object in the scene Hierarchy.

target = FindObjectOfType<EnemyMover>().transform;