NullReferenceException Error For Generating Rooms

I'm trying to make a game like Jetpack Joyride. But I'm having problems with the game generating rooms as the player moves on. My game runs perfectly fine in Unity, but when I build and run the game, I get the error: NullReferenceException at (wrapper managed-to-native) UnityEngine.Object:Internal_CloneSingle (UnityEngine.Object) at UnityEngine.Object.Instantiate[GameObject] (UnityEngine.GameObject original) [0x00017] in /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEngineObject.cs:202 at GeneratorScript.AddRoom (Single farhtestRoomEndX) [0x00018] in /Users/Matthew/Desktop/Unity Projects/Reeses Game/Reeses Game/Assets/Scripts/GeneratorScript.cs:51 at GeneratorScript.GenerateRoomIfRequred () [0x0013a] in /Users/Matthew/Desktop/Unity Projects/Reeses Game/Reeses Game/Assets/Scripts/GeneratorScript.cs:114 at GeneratorScript.FixedUpdate () [0x00002] in /Users/Matthew/Desktop/Unity Projects/Reeses Game/Reeses Game/Assets/Scripts/GeneratorScript.cs:39 (Filename: /Users/builduser/buildslave/unity/build/Runtime/Export/UnityEngineObject.cs Line: 202)

Here is the script I am using to generate the rooms:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class GeneratorScript : MonoBehaviour {
 
     public GameObject[] availableRooms;
 
     public List<GameObject> currentRooms;
 
     private float screenWidthInPoints;
 
     public GameObject[] availableObjects;    
     public List<GameObject> objects;
 
     public float objectsMinDistance = 5.0f;    
     public float objectsMaxDistance = 10.0f;
 
     public float objectsMinY = -1.4f;
     public float objectsMaxY = 1.4f;
 
     public float objectsMinRotation = -45.0f;
     public float objectsMaxRotation = 45.0f; 
 
 
     // Use this for initialization
     void Start () {
         float height = 2.0f * Camera.main.orthographicSize;
         screenWidthInPoints = height * Camera.main.aspect;
     }
 
     // Update is called once per frame
     void Update () {
 
     }
 
     void FixedUpdate () {
 
         GenerateRoomIfRequred();
 
         GenerateObjectsIfRequired();  
     }
 
 
     void AddRoom(float farhtestRoomEndX)
     {
         //1
         int randomRoomIndex = Random.Range(0, availableRooms.Length);
 
         //2
         GameObject room = (GameObject)Instantiate(availableRooms[randomRoomIndex]);
 
         //3
         float roomWidth = room.transform.FindChild("floor").localScale.x;
 
         //4
         float roomCenter = farhtestRoomEndX + roomWidth * 0.5f;
 
         //5
         room.transform.position = new Vector3(roomCenter, 0, 0);
 
         //6
         currentRooms.Add(room);            
     } 
 
     void GenerateRoomIfRequred()
     {
         //1
         List<GameObject> roomsToRemove = new List<GameObject>();
 
         //2
         bool addRooms = true;        
 
         //3
         float playerX = transform.position.x;
 
         //4
         float removeRoomX = playerX - screenWidthInPoints;        
 
         //5
         float addRoomX = playerX + screenWidthInPoints;
 
         //6
         float farhtestRoomEndX = 0;
 
         foreach(var room in currentRooms)
         {
             //7
             float roomWidth = room.transform.FindChild("floor").localScale.x;
             float roomStartX = room.transform.position.x - (roomWidth * 0.5f);    
             float roomEndX = roomStartX + roomWidth;                            
 
             //8
             if (roomStartX > addRoomX)
                 addRooms = false;
 
             //9
             if (roomEndX < removeRoomX)
                 roomsToRemove.Add(room);
 
             //10
             farhtestRoomEndX = Mathf.Max(farhtestRoomEndX, roomEndX);
         }
 
         //11
         foreach(var room in roomsToRemove)
         {
             currentRooms.Remove(room);
             Destroy(room);            
         }
 
         //12
         if (addRooms)
             AddRoom(farhtestRoomEndX);
     }
 
     void AddObject(float lastObjectX)
     {
         //1
         int randomIndex = Random.Range(0, availableObjects.Length);
 
         //2
         GameObject obj = (GameObject)Instantiate(availableObjects[randomIndex]);
 
         //3
         float objectPositionX = lastObjectX + Random.Range(objectsMinDistance, objectsMaxDistance);
         float randomY = Random.Range(objectsMinY, objectsMaxY);
         obj.transform.position = new Vector3(objectPositionX,randomY,0); 
 
         //4
         float rotation = Random.Range(objectsMinRotation, objectsMaxRotation);
         obj.transform.rotation = Quaternion.Euler(Vector3.forward * rotation);
 
         //5
         objects.Add(obj);            
     }
 
     void GenerateObjectsIfRequired()
     {
         //1
         float playerX = transform.position.x;        
         float removeObjectsX = playerX - screenWidthInPoints;
         float addObjectX = playerX + screenWidthInPoints;
         float farthestObjectX = 0;
 
         //2
         List<GameObject> objectsToRemove = new List<GameObject>();
 
         foreach (var obj in objects)
         {
             //3
             float objX = obj.transform.position.x;
 
             //4
             farthestObjectX = Mathf.Max(farthestObjectX, objX);
 
             //5
             if (objX < removeObjectsX)            
                 objectsToRemove.Add(obj);
         }
 
         //6
         foreach (var obj in objectsToRemove)
         {
             objects.Remove(obj);
             Destroy(obj);
         }
 
         //7
         if (farthestObjectX < addObjectX)
             AddObject(farthestObjectX);
     }
 
 }