Help with simple generation problem

Im trying to make a randomly generated road. I figured I could make several different types of road "tiles" that are the same size and write a script that puts these pieces together randomly each time. But I am new to programming and dont necessarily know how to do that so I wanted to start with a script that would just start with instantiating 5 roads onto my scene. I thought I had figured it out and I am getting a null reference exception error on the line where I have an if statement in my update function and I cant really figure out why... I have placed my code below so hopefully you can help... I have two separate classes, one( SpawnerManager) attached to an empty game object and RoadSpawner which is attached to each spawnpoint which is a child of every road.

 public class SpawnerManager : MonoBehaviour
 {
     public int spawnedRoads;
 
     public void AddRoad()
     {
         spawnedRoads++;
     }
 }
 public class RoadSpawner : MonoBehaviour
 {
     // Start is called before the first frame update
     public GameObject straightRoad;
     private bool isRoadSpawned = false;
     private SpawnerManager spawnManager;
     void Start()
     {
         
     }
 
     // Update is called once per frame
     void Update()
     {
         if(spawnManager.spawnedRoads < 5)
         {
             SpawnRoads();
         }
     }
 
     void SpawnRoads()
     {
         Instantiate(straightRoad);
         isRoadSpawned = true;
         spawnManager.AddRoad();
     }
 
     private void OnTriggerEnter(Collider other)
     {
         if (other.CompareTag("SpawnPoint") && other.GetComponent<RoadSpawner>().isRoadSpawned == true)
         {
             Destroy(gameObject);
         }
     }
 }