Script not working after restart unity, giving null exception

So i made one script to fill a roulette based in enums. The enum items will be the roulette items. The script it's work fine but when i restart unity it just give me null execeptions and i need to reset the script. When i do it's working properly again. But when i restart Unity it's giving me the same error.

this is the script:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 using System.Collections.Generic;
 
 [RequireComponent(typeof(EnumList))]
 public class RouletteUI : MonoBehaviour
 {
 
     internal enum RouletteDirection { UP = -1, DOWN = 1 };
 
     public List<Transform> _rouletteItemTransform;
     public GameObject _roulleteItemPrefab;
 
     System.Type m_T;
     public List<KeyValuePair<string, int>> m_Values;
     private int m_Index = 0;
 
     /// <summary>
     /// Describes the scroll amount in a given direction
     /// </summary>
     internal struct ScrollInfo
     {
         public float amount;
         public RouletteDirection _direction;
         public Vector3 _referencePosition;
         private Vector3 _lastPos;
 
         /// <summary>
         /// This method should be called when a drag action starts.
         /// </summary>
         /// <param name="pStartPosition"> is the mouse position at the beggining of the scroll action</param>
         public void BeginScrolling(Vector3 pStartPosition)
         {
             UpdateScrollAmount(pStartPosition);
             this._referencePosition = pStartPosition;
             this.amount = 0;
             this._direction = RouletteDirection.DOWN;
         }
 
         public void UpdateScrollAmount(Vector3 pMousePosition)
         {
 
             // are we changing direction ?
             if (pMousePosition.y > this._referencePosition.y && pMousePosition.y < this._lastPos.y)
             {
                 this._lastPos = this._referencePosition = pMousePosition;
                 this._direction = RouletteDirection.UP;
                 //Debug.Log("Direction changed! Now going UP.");
             }
 
             if (pMousePosition.y < this._referencePosition.y && pMousePosition.y > this._lastPos.y)
             {
                 this._referencePosition = pMousePosition;
                 this._direction = RouletteDirection.DOWN;
                 //Debug.Log("Direction changed! Now going DOWN.");
             }
 
             // Update the amount accordingly
             this.amount = this._referencePosition.y - pMousePosition.y;
             _lastPos = pMousePosition;
 
         }
     }
     public float _scrollSensitivity = 0.5f;
     public int _itemHeight = 30;
     public iTween.EaseType _animationType = iTween.EaseType.spring;
 
     private RectTransform _roulettePanel;
     private RectTransform _mainPanel;
     private RectTransform _selectorPanel;
     private ScrollInfo _scroll;
     private UnityEngine.EventSystems.EventTrigger _eventTrigger;
 
     // Selected element index
     private int selectedIndex = 4;
     private const string ROULETTE_PANEL_NAME = "RoulettePanel";
 
     public virtual void Start()
     {
         
         this._scroll = new ScrollInfo();
 
         // Find the roulette child panel
         _roulettePanel = transform.FindChild(ROULETTE_PANEL_NAME).GetComponent<RectTransform>();
 
         if (_roulettePanel == null)
             Debug.LogError(string.Format("Object '{0}' has no child named '{1}' with a RectTransform component attached to it", this.gameObject.name, ROULETTE_PANEL_NAME));
                 
         //Set all child element size to the desired one
         LayoutElement[] items = GetComponentsInChildren<LayoutElement>();
 
         foreach (LayoutElement e in items)
         {
             e.minHeight = e.preferredHeight = _itemHeight;
         }
 
         this._roulettePanel.transform.localPosition = Vector3.zero;
         InitializeRouleteItems();
     }
 
     public virtual void OnBeginDrag()
     {
     }
 
     public virtual void OnDrag()
     {
         this._scroll.UpdateScrollAmount(Input.mousePosition);
         ScrollRoulette(this._scroll);
     }  
     public virtual void OnEndDrag()
     {
     }
 
     private void ScrollRoulette(ScrollInfo pScrollInfo)
     {
         this._roulettePanel.Translate(Vector3.down * pScrollInfo.amount * _scrollSensitivity * Time.deltaTime);
 
     }  
 
     /// <summary>
     /// Instancia o prefab e cria os itens da roleta
     /// </summary>
     /// <param name="pText"></param>
     private void InstantiateRouletteItem(string pText)
     {
         GameObject item = Transform.Instantiate(_roulleteItemPrefab);
         item.transform.SetParent(_roulettePanel);
         item.GetComponent<Text>().text = pText;
 
         UnityEngine.UI.LayoutElement layout = item.AddComponent<UnityEngine.UI.LayoutElement>();
         layout.minHeight = _itemHeight;
         layout.preferredHeight = _itemHeight;
 
         _rouletteItemTransform.Add(item.transform);
     }
 
     protected void InitializeRouleteItems()
     {
         for (int i = 0; i < m_Values.Count; i++)
         {
             InstantiateRouletteItem(m_Values[i].Key);
         }
     }
 
     /// <summary>
     /// 
     /// </summary>
     /// <typeparam name = "T" ></ typeparam >
     public void InitializeWithEnum<T>() where T : System.IConvertible
     {
 
         if (!typeof(T).IsEnum) throw new System.ArgumentException("T must be an enumerated type");
 
         m_Values = new List<KeyValuePair<string, int>>();
         System.Array values = System.Enum.GetValues(typeof(T));
 
         foreach (object value in values)
         {
             string name = System.Enum.GetName(typeof(T), value);
             m_Values.Add(new KeyValuePair<string, int>(name, (int)value));
         }
         print("Selected Value" + GetSelectedString() + " : " + GetSelectedValue());
     }
 
     private int GetSelectedValue()
     {
         return m_Values[m_Index].Value;
     }
 
     private string GetSelectedString()
     {
         return m_Values[m_Index].Key;
     }
 }

So someone can help me with this?