NullReferenceException when setting Component as Variable, but no bugs

This is the code I'm currently using for a flag collectible in a platformer. The stage scrolls automatically, and each time the flag collectible leaves view, it's put into the object pool (controlled by different script). When it's reenabled, it's given a new random color. The color decides which animation is used, and changes the Start Color of the particle system. The Flag is an empty game object with an Animator, a Particle System, and this script.

 using UnityEngine;
 using System.Collections;
 
 public class Flag : MonoBehaviour {
 
     private Animator animator;
     private Renderer renderer;
     private ParticleSystem particle;
 
     public int maxcolor = 4;
     private Color myyellow = new Color(1f, 0.8f, 0f);
     private Color mygreen = new Color(0.45f, 0.8f, 0.3f);
     private Color myblue = new Color(0.1f, 0.65f, 0.87f);
     private Color myred = new Color(0.9f, 0.4f, 0.1f);
 
     public int flagColor;

     void Start()
     {
         renderer = transform.Find("flagSprite").GetComponent<Renderer>();
         animator = transform.Find("flagSprite").GetComponent<Animator>();
         particle = transform.Find("burst").GetComponent<ParticleSystem>();
 
         SetColor();
     }
 
     void OnEnable()
     {
         SetColor();
     }
 
     void OnDisable()
     {
         renderer.enabled = true;
     }
 
     void OnTriggerEnter2D(Collider2D other)
     {
         if (other.tag == "Player")
         {
             renderer.enabled = false;
             particle.Play();
         }
     }
 
     void SetColor()
     {
         flagColor = Random.Range(0, maxcolor);
         animator.SetInteger("flagColor", flagColor);
         
         switch(flagColor)
         {
             case 0: //yellow
                 particle.startColor = myyellow;
                 break;
             case 1: //green
                 particle.startColor = mygreen;
                 break;
             case 2: //blue
                 particle.startColor = myblue;
                 break;
             case 3: //red
                 particle.startColor = myred;
                 break;
         }
     }
 }

Everything works as intended. There's no gameplay issue or noticeable bug, but I'm getting a NullReferenceException the first time renderer, particle, or animator is used. I can get rid of this error by replacing

 animator.SetInteger("flagColor", flagColor);

with

 transform.Find("flagSprite").GetComponent<Animator>().SetInteger("flagColor", flagColor);

but I shouldn't have to do that EVERY TIME, right? That's the point of storing the component in a variable.

EDIT: I get the NullReferenceException with the variables renderer, animator, and particle unless I replace all uses with with the full GetComponent.