Object reference not set to an instance of an object

I keep getting this error after I expanded my spawning class.

NullReferenceException: Object reference not set to an instance of an object Spawner.SpawnEnemy () (at Assets/Scripts/Spawner.cs:23) SpawnController.startWave () (at Assets/Scripts/SpawnController.cs:47) SpawnController.waveController () (at Assets/Scripts/SpawnController.cs:29)

Bellow you will find my Enemy Spawn and SpawnManager classes. Any help would be appreciated, this is driving me bonkers.

using UnityEngine; using System.Collections;

public class Spawner : MonoBehaviour {

 public GameObject Enemy;
 GameObject[] objs;
 int top;

 void Start()
 {
     objs = GameObject.FindGameObjectsWithTag("Spawn_Point");
     top = objs.Length;
  //      InvokeRepeating("SpawnEnemy", 0.01f, 5.0f);
 }

 void Update()
 {
 }

 public void SpawnEnemy()
 {
     Instantiate(Enemy, RandomCircle(objs[Random.Range(0, top)].GetComponent<Transform>().position, 5), Quaternion.identity);
     SpawnController.numAlive++;
 }

 Vector3 RandomCircle(Vector3 center, float radius)
 {
     float ang = Random.value * 360;
     Vector3 pos;
     pos.x = center.x + radius * Mathf.Sin(ang * Mathf.Deg2Rad);
     pos.y = center.y;
     pos.z = center.z + radius * Mathf.Cos(ang * Mathf.Deg2Rad);
     return pos;
 }

}

 using UnityEngine;
 using System.Collections;
 
 public class SpawnController : Spawner {
 
     public static int numAlive;
     int round;
     bool active;
 
     // Use this for initialization
     void Start () {
         numAlive = 0;
         round = 0;
         active = false;
         InvokeRepeating("waveController", 0.01f, 15.0f);
     }
     
     // Update is called once per frame
     void Update ()
     {
     }
 
     void waveController()
     {
         if(!active)
         {
             Debug.Log("Active now = true");
             active = true;
             startWave();
         }
         else
         {
             if(numAlive == 0)
             {
                 Debug.Log(" End round ");
                 active = false;
                 round++;
             }
         }
     }



   
 using UnityEngine;
 using System.Collections;
 
 namespace SpawningFramework
 {
     public class Enemy : MonoBehaviour
     {
 
         public float MaxHealth;
         float health;
         Vector3 pos;
 
 
         [HideInInspector]
         public bool alive;
 
         void Update()
         {
         }
 
         /// Called when this enemy has been spawned
         void Start()
         {
             health = MaxHealth;
             alive = true;
             pos = transform.position;
             
             InvokeRepeating("move", 0.01f, .2f);
 
         }
 
         void move()
         {
            // transform.Translate(0, 0.025f, 0);
         }
 
         /// Called when the player loses
         public virtual void OnGameOver()
         {
         }
 
         void OnTriggerEnter(Collider other)
         {
             Debug.Log(other.tag);
             if (other.tag == ("Player"))
             {
                 Hurt(54);
 //              Destroy(other.gameObject);        
             }
         }
 
         #region Taking Damage
         /// Hurts the enemy and returns if it dies or not
         public virtual bool Hurt(float damage)
         {
             if (!alive)
                 return false;//exit if dead
 
             health -= damage;//hurt the enemy
 
             if (health < 0.1)
             {
                 alive = false;
                 SpawnController.numAlive--;
                 Destroy(this.gameObject);
                 Destroy(this);
                 return true;
             }
 
             return health < 0.1;//return if this will die
         }
 
 
         #endregion
     }
 }
 
 
     void startWave()
     {
         Debug.Log("Starting wave: " + round);
         for(int i = 0; i < (8 + 2 * round); i++)
         {
             SpawnEnemy();
         }
     }
 }