instantiate a gameobject since another script

Hello people, I have a small problem.

In fact I would want to instantiate a gameobject since another script.

Here is the error that I reçoi:NullReferenceException: Object references not set to the year authority of the object year GenDongeon.geng () (at Assets Assets/Scripts/GenDongeon.cs:30 Scripts) GenDongeon+pause > c __ Iterator0. MoveNext () (at Assets Assets/Scripts/GenDongeon.cs:21 Scripts)

Thank you.

Sorry for my bad English, because I am French.

Script Salles :

 using UnityEngine;
 using System.Collections;
 
 public class Salles : MonoBehaviour {
 
     public GameObject [] salleg1;
     public GameObject [] salled1;
     public GameObject [] salleu1;
     public GameObject [] salleb1;
 
     public static GameObject [] salleg;
     public static GameObject [] salled;
     public static GameObject [] salleu;
     public static GameObject [] salleb;
 
     public static int salg;
     public static int sald;
     public static int salu;
     public static int salb;
 
     void start(){
 
         salleg = new GameObject[salleg1.Length];
         salled = new GameObject[salled1.Length];
         salleu = new GameObject[salleu1.Length];
         salleb = new GameObject[salleb1.Length];
 
         salg = salleg1.Length;
         sald = salled1.Length;
         salu = salleu1.Length;
         salb = salleb1.Length;
 
         for(int a=0;a<salleg1.Length;a++){
             salleg[a] = salleg1[a];
         }
         for(int b=0;b<salled1.Length;b++){
             salled[b] = salled1[b];
         }
         for(int c=0;c<salleu1.Length;c++){
             salleu[c] = salleu1[c];
         }
         for(int d=0;d<salleb1.Length;d++){
             salleb[d] = salleb1[d];
         }
     }
 }

Script GenDongeon :

 using UnityEngine;
 using System.Collections;
 
 public class GenDongeon : MonoBehaviour {
 
     public bool g;
     public bool d;
     public bool u;
     public bool b;
 
     public int timep;
 
     void Start () {
 
         StartCoroutine (pause());
 
     }
 
     public IEnumerator pause(){
         yield return new WaitForSeconds(timep);
         geng();
         gend();
         genu();
         genb();
     }
 
     void geng(){
         if(g==true){
             int rand = Random.Range (0,Salles.sald);
             Instantiate (Salles.salled[rand],new Vector3(this.transform.position.x-8,this.transform.position.y,0),Quaternion.identity);
         }
     }
 
     void gend(){
         if(d==true){
             int rand = Random.Range (0,Salles.salg);
             Instantiate (Salles.salleg[rand],new Vector3(this.transform.position.x+8,this.transform.position.y,0),Quaternion.identity);
         }
     }
 
     void genu(){
         if(u==true){
             int rand = Random.Range (0,Salles.salb);
             Instantiate (Salles.salleb[rand],new Vector3(this.transform.position.x,this.transform.position.y+8,0),Quaternion.identity);
         }
     }
 
     void genb(){
         if(b==true){
             int rand = Random.Range (0,Salles.salu);
             Instantiate (Salles.salleu[rand],new Vector3(this.transform.position.x,this.transform.position.y-8,0),Quaternion.identity);
         }
     }
 }