Why does this work but this doesn't even though they are the same thing?

In my game I am trying to trigger the death animation but it doesn't work when I use anim.SetBool("isDead", true); however when I use GetComponent().SetBool("isDead", true); it works. I initialized anim by doing this: private Animator anim; and in Start anim = this.gameObject.GetComponent();. Then I did the previous code and only the getcomponenet works. When I do anim.SetBool("isDead", true); it gives an NullRefrenceExeption Errror. The isDead bool is a actual variable in the animator.

This is the script: (The important parts will have comments beside them saying important):

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.SceneManagement;
 using UnityEngine;
 using UnityEngine.AI;
 
 public class Enemy
 {
     public float health;
     public float speed;
     public NavMeshAgent agent;
     public float inRange;
     public float inView;
     
 
     public Enemy(float health, float speed, NavMeshAgent agent, float inRange, float inView)
     {
         this.health = health;
         this.speed = speed;
         this.agent = agent;
         this.inRange = inRange;
         this.inView = inView;
         
     }
 }
 
 public class EnemyBaseScript : MonoBehaviour
 {
     public float health;
     public float speed;
     public NavMeshAgent agent;
     public float inRange;
     public float inView;    
     public Enemy enemy;
     public GameObject self;
     public bool MultiAttack = false;
 
     public GameObject playerPos;
 
     private float SelectedDif;
         
     private Animator anim; //important
 
     private PlayerPos pl;
     private Weapon weaponGettingHitBy;
     private TakeDamage tk;
     private TimeToFight TtF;
     private Difficulty dif;
     private GameObject buttonController;
 
     // Start is called before the first frame update
     void Start()
     {
         pl = GetComponent<PlayerPos>();
         tk = GetComponent<TakeDamage>();
         TtF = GetComponent<TimeToFight>();
         dif = GetComponent<Difficulty>();
         buttonController = GameObject.FindGameObjectWithTag("ButtonController");
 
         SelectedDif = buttonController.GetComponent<Difficulty>().difficulty;
         SceneManager.UnloadSceneAsync("DifficultyChosing");
 
         health = health * SelectedDif;
         speed = speed * SelectedDif;
         inRange = inRange * SelectedDif;
         inView = inView * SelectedDif;
         
 
         enemy = new Enemy(health, speed, agent, inRange, inView);
         agent = gameObject.GetComponent<NavMeshAgent>();
         self = this.gameObject;
 
         anim = this.gameObject.GetComponent<Animator>(); //important
     }
 
     public void Update()
     {
         Invoke("LookForPlayer", 5.0f);
        
         if (PlayerPos.FindPlayerPos(inRange, playerPos, inView, self))
         {
            TimeToFight.ChoseChasingWhatStateToAttackPlayer(agent, playerPos, self, anim, MultiAttack);           
         }
         
         if (health < 0.1f)
         {
             StartCoroutine(JustDies());            
         }
     }    
         
     IEnumerator JustDies() //important
     {
         //anim.SetBool("isDead", true);
         GetComponent<Animator>().SetBool("isDead", true);
 
         yield return new WaitForSeconds(4.5f);
         Destroy(this.gameObject);
     }
 
     public GameObject LookForPlayer()
     {
         playerPos = GameObject.FindGameObjectWithTag("Player");
         return playerPos;
     }
 
     private void OnTriggerEnter(Collider col)
     {
         if (col.gameObject.tag == "Weapon")
         {
             weaponGettingHitBy = new Weapon(col.gameObject, col.gameObject.GetComponent<WeaponBaseScript>().damagedealing);
             health = TakeDamage.TakeDmg(health, weaponGettingHitBy);
         }
     }
 }