Get transform of an instantiated GameObject(clone)

Hi, i have a problem with get the transform of an instantiated Gameobject(clone), i wanna get the trasform to use it in other script, i only achieve a null reference.

public class Enemy : MonoBehaviour {

	
	public float activeZone;
	float nextFire;
    public float Distance;
	public Transform player;
	public Transform FirePosition;
	 Transform enemy;
	GameObject Bullet;
	 Vector2 posPlayer;
	 Vector2 posBullet;

	
	
	void Start () 
	{
		nextFire = 0f;
		activeZone = 12f;
		player = GameObject.FindGameObjectWithTag ("Player").transform;
		FirePosition = GameObject.FindGameObjectWithTag ("Fire").transform;
		Bullet = GameObject.FindGameObjectWithTag("Bullets");

	}
	
	// Update is called once per frame
	void Update () 
	{

		if (Distance < activeZone) {
			
			if (Input.GetKeyDown (KeyCode.F) && Time.time > nextFire + 2.0f) {

				nextFire = Time.time;
				GameObject BulletInstance;
				BulletInstance = Instantiate (Bullet,FirePosition.position, FirePosition.rotation) as GameObject;
				BulletInstance.rigidbody2D.AddForce (new Vector2 (-5000f, -30f));
				enemy = BulletInstance.transform;
				Destroy(BulletInstance,0.5f);
			}	
		}
				
		}
		

	void FixedUpdate()
	{

		posPlayer = player.position;
		posBullet = FirePosition.position;
		Distance = Vector2.Distance (posPlayer, posBullet);
    }

Try finding it directly after you instantiate it:

enemy = GameObject.Find(“Bullet(Clone)”).transform;