Stop object spawning on top of each other?

i have this function that spawns enemies in random positions i noticed that they sometimes spawn on top of each other so i tried to use vector2.distance, to compare the old enemy position by the new enemy position but it wont work come up with a error telling me my script is trying to access a object with null this is the code.

 function spawnenemytype (enemytype:GameObject, amount:int)
 
 {
 
 var spawnLocation:Vector3;
 
 var temp:int;
 isSpawning = true;
 var pos:Vector2 = Vector2.zero;
 
 for (var k:int = 0; k < 1000; k++)
 {
         var randomX:float = Random.Range(minX, maxX);
         var randomY:float = Random.Range(minY, maxY);
         pos = new Vector2(randomX, randomY);
         
 for ( var i:int = 0; i < amount; i++)
 {
     yield WaitForSeconds(1);
  
     temp = Random.Range(1,5);
 
     if (temp == 1)
     {    
         if (spawnedEnemies.Count == 0)
         {
             spawnLocation = new Vector3(pos.x,playerY + offset.y,0);
         }
         else if (Vector2.Distance(spawnLocation , tempGO[i].transform.position) < threshold)
         {    
              break;
          }
     }
 
     if (temp == 2)
     {
 
          if (spawnedEnemies.Count == 0)
         {
             spawnLocation = new Vector3(pos.x,playerY + offset.y,0);
         }
         else if (Vector2.Distance(spawnLocation , tempGO[i].transform.position) < threshold)
         {    
              break;
          }
          
     }
 
 
     if (temp == 3)
     {    
 
          if (spawnedEnemies.Count == 0)
         {
             spawnLocation = new Vector3(pos.x,playerY + offset.y,0);
         }
         else if (Vector2.Distance(spawnLocation , tempGO[i].transform.position) < threshold)
         {    
              break;
          }
          
     }
 
     if (temp == 4)
     {
 
          
          if (spawnedEnemies.Count == 0)
         {
             spawnLocation = new Vector3(pos.x,playerY + offset.y,0);
         }
         else if (Vector2.Distance(spawnLocation , tempGO[i].transform.position) < threshold)
         {    
              break;
          }
          //spawnLocation = new Vector3(newPosition.x,playerY+offset.y,0);
          //Debug.Log("Creating enemy number4: " );
          
     }
 
  
 tempGO[i] = Instantiate(enemytype,spawnLocation,Quaternion.identity);
 spawnedEnemies.Add(tempGO[i]);
 
 //Debug.Log("how many enemies "+spawnedEnemies.Count);
  enemycounter++;
  
 }
 }
 
 isSpawning = false;
 
 
 
 }