C# Referencing a Non-Static Variable Help

ok so me and a few friends have started working on this game and i was put in charge of programming. anyway i was working on a way to add multiple enemies into a scene, and needed to get rid of the static variable that i was currently using as a place holder. now when i shoot an enemy i get a null reference pointer error. please help :)

GunScript Code

 using UnityEngine;
 using System.Collections;
 
 public class GunScript : MonoBehaviour {
     
     /**
      * Next Objective is making a list to organize the guns and make this script the only script for guns.
      * */
     
     //How much damage the gun does.
     public int dmg;
     //How long the muzzle flash lasts.
     public float delay;
     //Stores if the raycast hit an object.
     RaycastHit hit;
     //How fast the bullet travels (Not implemented yet).
     public float bulletSpeed;
     //How much ammo the clip can hold.
     public int clipSize;
     //Used to display where the ammo counter is located.
     public float pixDown;
     public float pixRight;
     //How much Ammunition is currently in the gun.
     public int Ammo;
     //Used to display the particle system of the muzzle flash (will be switching to a 2D texture soon).
     public ParticleSystem muzzelFlash;
     //Holds the light that appears when a gun is shot.
     public Light muzzelLight;
     //Stores the audio clip of the gun shot.
     public AudioClip shot;
     //Stores the audio clip of the reloading sound.
     public AudioClip reloadSound;
     //How long the muzzle flash lasts.
     float flashTime = 0.05f;
     //How long the gun takes to reload.
     public float reloadTime;
     //Used to style the gui of the ammo counter.
     public GUIStyle text = new GUIStyle();
     //Checks to see if the gun is reloading.
     bool isReloading;
     //Used to call Enemy Health from the EnemyAI script.
     public EnemyAI enemy;
     
     // Use this for initialization
     void Start () {
         //Makes sure that the muzzle flash is off.
         muzzelFlash.renderer.enabled = false;
         muzzelLight.enabled = false;
         //Gets the enemy ai script.
         enemy = GetComponent<EnemyAI>();
     }
     
     // Update is called once per frame
     void Update () {
         //Fires When Mouse1 is pressed.
         if(Input.GetButtonDown("Fire1") && Ammo > 0 && isReloading == false)
         {
             //Plays the shot sound when fired.
             audio.PlayOneShot(shot);
             //Subtracts one from the ammo counter.
             Ammo = Ammo - 1;
             StartCoroutine(Shoot());
             
             //Not working :(
             if(Input.GetKeyDown("r")){
                 Debug.Log("Button Pressed");
                 StartCoroutine(Reload());
             }
         }
     }
     
     //Displays ammo in clip
     void OnGUI(){
         //Displays the current ammo in the gun clip.
         GUI.Label(new Rect(Screen.width * pixRight, Screen.height * pixDown, 100, 20), "" + Ammo, text);
     }
     
     //Fires Gun Off
     IEnumerator Shoot()
     {
         //Enables muzzel flash.
         muzzelFlash.renderer.enabled = true;
         muzzelLight.enabled = true;
     
         //Enables the raycast.
         if(Physics.Raycast(transform.position, transform.forward, out hit, 100)){
             //Draws a line in the scene view to see where the bullet hit, if it hit.
             Debug.DrawLine(transform.position, hit.point, Color.green, 0.3f);
             //Checks to see if the raycast hit an Enemy. If so than do damage to the enemy.
             if(hit.collider.gameObject.tag == "Enemy"){
             enemy.health -= dmg;
             }
         }
         //Waits for however long the flashTime is.
         yield return new WaitForSeconds(flashTime);
         //Disables muzzle flash.
         muzzelFlash.renderer.enabled = false;
         muzzelLight.enabled = false;
         
         //Checks to see if the gun is out of ammo. If so then run the Reload function.
         if(Ammo == 0)
             StartCoroutine(Reload());
     }
     
     //Reloading function (will add animation eventually).
     public IEnumerator Reload()
     {
         //Changes the boolean "isReloading" to true to symbolize that the gun is reloading.
         isReloading = true;
         //Plays the reloading sound.
         audio.PlayOneShot(reloadSound);
         //Waits for the reload time to be complete.
         yield return new WaitForSeconds(reloadTime);
         //Changes the ammo to full
         Ammo = clipSize;
         //Changes the boolean "isReloading" to false to symbolize that the gun is not reloading.
         isReloading = false;
     }
     
 }

And the EnemyAI Script

 using UnityEngine;
 using System.Collections;
 
 public class EnemyAI : MonoBehaviour {
     
     //The distance at which AI can attack the player.
     public int startAttack;
     //Determines if the player is under attack.
     bool attack;
     //How long between the AI's attacks
     public int attackTimer;
     //Distance at which the AI will start.
     public int startAttackDistance;
     //Who the AI will attack.
     public Transform target;
     //Move speed of the AI.
     public float moveSpeed;
     //Rotation speed of the AI.
     public float rotationSpeed;
     //Used to find the cube's position.
     public Transform myTransform;
     //Cubes Health.
     public float health = 10;
     
     
     void Awake(){
         //Targets Player once level is started.
         target = GameObject.FindGameObjectWithTag("Player").transform;
     }
     // Use this for initialization
     void Start () {
         //Used to find the AI's position.
         myTransform = transform;
     }
     
     // Update is called once per frame
     void Update () {
                 
         //Used to determine if the player is close enough to the AI to engage an attack.
         float distance = (target.position - myTransform.position).magnitude;
         
         //Starts the AI attack.
         if(distance < startAttackDistance){
             
             //Draws a line in the scene to show what the AI is targeting.
             Debug.DrawLine(myTransform.position, target.position, Color.cyan);
         //Rotates towards the player.
         myTransform.rotation = Quaternion.Slerp(myTransform.rotation, Quaternion.LookRotation(target.position - myTransform.position), rotationSpeed * Time.deltaTime);
         
         //Moves toward the player.
         myTransform.position += myTransform.forward * moveSpeed * Time.deltaTime;
                         
             if(distance <= startAttack && attack == false)
                 StartCoroutine(Attack());
         }
         //Checks to see the health of the AI. If it is 0, then destroy the AI.
         if(health <= 0)
             Destroy(gameObject);
         if(health < 0)
             health = 0;
     }
     
     IEnumerator Attack(){
         attack = true;
         yield return new WaitForSeconds(attackTimer);
         PlayerHealth.playerHealth -=1;
         attack = false;
     }
     
     public void Damage(){
         health -= 1;
     }    
 }