This script was functioning perfectly then i turned it back on and it is giving me a null reference error

using UnityEngine; using System.Collections;

public class Zombie_controller : MonoBehaviour {

 NavMeshAgent zombie;
 Animator anim;
 AudioSource aud;
 EnemyHealth enemyhealth;
 public float timeBetweenAttacks = .5f;
 public int attackDamage = 10;
 GameObject Player;
 GameObject BO;
 GameObject BO1;
 GameObject BO2;
 GameObject BO3;
 GameObject BO4;
 GameObject BO5;


 setGameboard set;

 WoodenBoardHealth HealthWood;
 WoodenBoardHealth HealthWood1;
 WoodenBoardHealth HealthWood2;
 WoodenBoardHealth HealthWood3;
 WoodenBoardHealth HealthWood4;
 WoodenBoardHealth HealthWood5;
 bool playerInRange;
 bool boardInRange;
 bool boardInRange1;
 bool boardInRange2;
 bool boardInRange3;
 bool boardInRange4;
 bool boardInRange5;
 playerHealth PlayerHealth;
 public Transform thePoint;



 public float timer;




 void Start () {



     BO = GameObject.FindGameObjectWithTag ("WoodenBoard");
     BO1 = GameObject.FindGameObjectWithTag ("WoodenBoard1");
     BO2 = GameObject.FindGameObjectWithTag ("WoodenBoard2");
     BO3 = GameObject.FindGameObjectWithTag ("Wooden Board3");
     BO4 = GameObject.FindGameObjectWithTag ("Wooden Board4");
     BO5 = GameObject.FindGameObjectWithTag ("Wooden Board5");

     HealthWood = BO.GetComponent<WoodenBoardHealth> ();
     HealthWood1 = BO1.GetComponent<WoodenBoardHealth> ();
     HealthWood2 = BO2.GetComponent<WoodenBoardHealth> ();
     HealthWood3 = BO3.GetComponent<WoodenBoardHealth> ();
     HealthWood4 = BO4.GetComponent<WoodenBoardHealth> ();
     HealthWood5 = BO5.GetComponent<WoodenBoardHealth> ();
     Player = GameObject.FindGameObjectWithTag ("Player");
     PlayerHealth = Player.GetComponent <playerHealth> ();
     aud = GetComponent<AudioSource> ();
     anim = GetComponent<Animator> ();
     enemyhealth = GetComponent<EnemyHealth> ();

     set = GetComponent<setGameboard> ();

     zombie = GetComponent<NavMeshAgent> ();
 }
 

 void Update () {
     timer += Time.deltaTime;

     zombie.SetDestination (thePoint.position);


     if (timer >= timeBetweenAttacks && playerInRange) {
         Attack ();
     }









     if (timer >= timeBetweenAttacks && boardInRange ) {
         SmashWood ();
         HealthWood.Smashing.Play ();
     }
     if (timer >= timeBetweenAttacks && boardInRange1) {
         SmashWood1 ();
         HealthWood1.Smashing.Play ();
     }
     if (timer >= timeBetweenAttacks && boardInRange2) {
         SmashWood2 ();
         HealthWood2.Smashing.Play ();
     }
     if (timer >= timeBetweenAttacks && boardInRange3) {
         SmashWood3 ();
         HealthWood3.Smashing.Play ();
     }
     if (timer >= timeBetweenAttacks && boardInRange4) {
         SmashWood4 ();
         HealthWood4.Smashing.Play ();
     }
     if (timer >= timeBetweenAttacks && boardInRange5) {
         SmashWood5 ();
         HealthWood5.Smashing.Play ();
     }











     if (HealthWood.ISsmashed == true) {
         zombie.enabled = true;
     }
     if (HealthWood1.ISsmashed == true) {
         zombie.enabled = true;
     }
     if (HealthWood2.ISsmashed == true) {
         zombie.enabled = true;
     }
     if (HealthWood3.ISsmashed == true) {
         zombie.enabled = true;
     }
     if (HealthWood4.ISsmashed == true) {
         zombie.enabled = true;
     }
     if (HealthWood5.ISsmashed == true) {
         zombie.enabled = true;
     }



     playerInRange = false;

 
     }

 void OnTriggerEnter (Collider other)
 {
     if (other.gameObject.CompareTag ("Player")) {
         playerInRange = true;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if(other.gameObject.CompareTag ("WoodenBoard")){
         boardInRange = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if(other.gameObject.CompareTag ("WoodenBoard1")){
         boardInRange1 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if(other.gameObject.CompareTag ("WoodenBoard2")){
         boardInRange2 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if(other.gameObject.CompareTag ("Wooden Board3")){
         boardInRange3 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if(other.gameObject.CompareTag ("Wooden Board4")){
         boardInRange4 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if(other.gameObject.CompareTag ("Wooden Board5")){
         boardInRange5 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
 }

 void OnTriggerStay (Collider other)
 {
     if (other.gameObject.CompareTag ("Player")) {
         playerInRange = true;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if (other.gameObject.CompareTag ("WoodenBoard")) {
         boardInRange = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
         }
     if (other.gameObject.CompareTag ("WoodenBoard1")) {
         boardInRange1 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");    
     }
     if (other.gameObject.CompareTag ("WoodenBoard2")) {
         boardInRange2 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if (other.gameObject.CompareTag ("Wooden Board3")) {
         boardInRange3 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if (other.gameObject.CompareTag ("Wooden Board4")) {
         boardInRange4 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");
     }
     if (other.gameObject.CompareTag ("Wooden Board5")) {
         boardInRange5 = true;
         zombie.enabled = false;
         anim.SetTrigger ("Attack");
         anim.Play ("zombie_attack");        
     }
 }
         
     void Attack ()
     {
     timer = 0f;
     
     if(PlayerHealth.currentHealth > 0)
     {
         PlayerHealth.TakeDamage (attackDamage);
     }
     }
 void SmashWood (){
     timer = 0f;
     if (HealthWood.CurrHealth > 0) {
         HealthWood.FuckingHit (attackDamage);

     }
 }
 void SmashWood1(){
     timer = 0f;
     if (HealthWood1.CurrHealth > 0) {
         HealthWood1.FuckingHit (attackDamage);
         }
     }
     void SmashWood2(){
     timer = 0f;
     if (HealthWood2.CurrHealth > 0) {
         HealthWood2.FuckingHit (attackDamage);
     }
 }
     void SmashWood3(){
     timer = 0f;
     if (HealthWood3.CurrHealth > 0) {
         HealthWood3.FuckingHit (attackDamage);
     }
 }
     void SmashWood4(){
     timer = 0f;
     if (HealthWood4.CurrHealth > 0) {
         HealthWood4.FuckingHit (attackDamage);
     }
 }
     void SmashWood5(){
     timer = 0f;
     if (HealthWood5.CurrHealth > 0) {
         HealthWood5.FuckingHit (attackDamage);
     }

}

}

So my problem occurs at line 78 where i set the destination for the NavMeshAgent. As you can see I'm using a public transform so i insert the target in the inspector, but then it tells me there's a null reference please help.