Health not being subtracked.

I have the following code and it is basically my AI system fro my enemy. It controls targeting and attacking. I just added the attack() but I am get a the following error. In the health script it is trying to axcess is called ShipHealth.cs and this is where I am trying to send the information :

public void AddjustCurrentHealth(int adj)

NullReferenceException: Object reference not set to an instance of an object EnemyAi.attack () EnemyAi.cs:109)

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic; 
 
 public class EnemyAi : MonoBehaviour 
 {
     //public Transform target;//Targets.
     public int rotationSpeed;//Speed enemy can rotate.
     public List<Transform> targets = new List<Transform>();//List of targets.
     public GameObject Gun;//Where the laser could come from.
     public int Damage = -10;//This should be negative or you are going to heal it.
     //public GameObject target;
     private LineRenderer LR;
     
     private float arcLength = 2.0f;
     private float arcVariation = 0f;
     private float inaccuracy = 0f;
     
     private Vector3 fwd;
 
     
     
     private Transform myTransform;//Save for the transform.
     void Start()
     {
         LR  = Gun.GetComponent<LineRenderer>();
 
     }
     void Awake()
     {
         
         myTransform = transform;//This saves our transform so we dont have to look it up all the time.    
         
         
     }
     
     void Update ()
     {
         
         if(targets.Count < 1) 
         {
             Gun.GetComponent<LineRenderer>().enabled = false;
             return;//If there is no targets sets targets to 0.
         }
         
         myTransform.rotation = Quaternion.Slerp(myTransform.rotation, Quaternion.LookRotation(targets[0].position - myTransform.position), rotationSpeed * Time.deltaTime);//Makes it look at us using the speed we set over time.
         
         Laser();
         attack();
         
  }
     void Laser()
     {
         Vector3 lastPoint = transform.position;
         
         
         int i = 1;
 
         LR.SetPosition(0, transform.position);//make the origin of the LR the same as the transform   
          while (Vector3.Distance(targets[0].transform.position, lastPoint) >.5) 
              {//was the last arc not touching the target?            
                  LR.SetVertexCount(i + 1);//then we need a new vertex in our line renderer          
                  fwd = targets[0].transform.position - lastPoint;//gives the direction to our target from the end of the last arc20.         
                  fwd.Normalize();//makes the direction to scale         
                   fwd = Randomize(fwd, inaccuracy);//we don't want a straight line to the target though      
                   fwd *= Random.Range(arcLength * arcVariation, arcLength);//nature is never too uniform    
                  fwd += lastPoint;//point + distance * direction = new point. this is where our new arc ends     
                   LR.SetPosition(i, fwd);//this tells the line renderer where to draw to25.         
                  i++;         
                  lastPoint = fwd;//so we know where we are starting from for the next arc  
               }
         
     }
      Vector3 Randomize(Vector3 v3 ,   float inaccuracy2)
     {
         
         v3 += new Vector3(Random.Range(-1.0f, 1.0f), Random.Range(-1.0f, 1.0f), Random.Range(-1.0f, 1.0f)) * inaccuracy2; 
           v3.Normalize(); 
            return v3; 
         
     }
         
     
     
      void OnTriggerEnter(Collider other) //When somthing enters the trigger.
     {
         if(other.tag == "Player")//Check if it was tagged player.
         {
             targets.Add(other.transform);//If so add it to the targets list.
             Gun.GetComponent<LineRenderer>().enabled = true;
         }
         
         
     }
     void OnTriggerExit(Collider other) //When somthing exits the trigger.
     {
         if(other.tag == "Player")//Check if it was tagged player.
         {
             targets.Remove(other.transform);//If so remove it from the targets list
             
         }
         
         
     }
     private void attack()
     {
         print("I have made it this far");
         ShipHealth sh = (ShipHealth)targets[0].GetComponent("ShipHeatlh");
         sh.AddjustCurrentHealth(Damage);
         
     }
     
     
 }