Object reference not set to an instance of an object.

I am trying to make a wall deactivate and then reactivate ,but I get this error

Object reference not set to an instance of an object
ResetFinish.OnTriggerEnter2D (UnityEngine.Collider2D other) (at Assets/Scripts/ResetFinish.cs:15)

CODE:

public class ResetFinish : MonoBehaviour {

public GameObject line;
public GameObject Line;

void OnTriggerEnter2D(Collider2D other) {
	line = GameObject.Find ("Line");
	Line = GameObject.Find ("FinishLine");

	GameObject.Find ("Finish");
	if (other.gameObject.CompareTag ("Player")) {
		line.gameObject.SetActive (true);
		Line.gameObject.SetActive (true);
	}
}

}

Make sure you have a GameObject in your scene named “Line” and another one named “FinishLine”.

You can remove line 8: "GameObject.Find(“Finish”); as it is doing nothing.