how to solve -- Object reference not set to an instance of an object -- ?

At the end of my level there is a sign that when you touch it will bring you to the world map. In this script that is attached to the sign i activate a bool "LVL1_1_Completed "

Script on sign using UnityEngine; using System.Collections;

public class WinLVL1_1 : MonoBehaviour {

 public bool LVL1_1_Completed;


 void Start ()
 {
     
 }
 
 void Update ()
 {
     
 }


 void OnTriggerEnter2D(Collider2D other)
 {
     if (other.tag == "Player")
     {
         PlayerHealth PlayerWins = other.gameObject.GetComponent<PlayerHealth> ();
         PlayerWins.WinGame ();

         LVL1_1_Completed = true;
     }
 }

}

On the canvas of the world map i have a script that must check if the bool is true .... if it is true the next level must be unlocked.

Script on world map using UnityEngine; using System.Collections;

public class UnlockLevels : MonoBehaviour {

 public GameObject UnlockLVL_1_2;


 void Start ()
 {
     
 }

 void Update ()
 {
     if (GameObject.Find("SignLVL_1_1").GetComponent<WinLVL1_1>().LVL1_1_Completed)
     {
         UnlockLVL_1_2.SetActive (true);
     }
 }

}

When i hit play it gives me an error that says "Object reference not set to an instance of an object" in the line "if (GameObject.Find("SignLVL_1_1").GetComponent().LVL1_1_Completed)".

Please help me with this ;p