Unity3D screen fading script (using new UI)

FadeInOut.cs

using UnityEngine;
using UnityEngine.UI;
using System.Collections;
using UnityEngine.SceneManagement;

public class ScreenFader : MonoBehaviour
{
    public Image FadeImg;
    public float fadeSpeed = 1.5f;
    public bool sceneStarting = true;


    void Awake()
    {
        FadeImg.rectTransform.localScale = new Vector2(Screen.width, Screen.height);
    }

    void Update()
    {
        // If the scene is starting...
        if (sceneStarting)
            // ... call the StartScene function.
            StartScene();
    }


    void FadeToClear()
    {
        // Lerp the colour of the image between itself and transparent.
        FadeImg.color = Color.Lerp(FadeImg.color, Color.clear, fadeSpeed * Time.deltaTime);
    }


    void FadeToBlack()
    {
        // Lerp the colour of the image between itself and black.
        FadeImg.color = Color.Lerp(FadeImg.color, Color.black, fadeSpeed * Time.deltaTime);
    }


    void StartScene()
    {
        // Fade the texture to clear.
        FadeToClear();

        // If the texture is almost clear...
        if (FadeImg.color.a <= 0.05f)
        {
            // ... set the colour to clear and disable the RawImage.
            FadeImg.color = Color.clear;
            FadeImg.enabled = false;

            // The scene is no longer starting.
            sceneStarting = false;
        }
    }


    public IEnumerator EndSceneRoutine(int SceneNumber)
    {
        // Make sure the RawImage is enabled.
        FadeImg.enabled = true;
        do
        {
            // Start fading towards black.
            FadeToBlack();

            // If the screen is almost black...
            if (FadeImg.color.a >= 0.95f)
            {
                // ... reload the level
                SceneManager.LoadScene(SceneNumber);
                yield break;
            }
            else
            {
                yield return null;
            }
        } while (true);
    }

    public void EndScene(int SceneNumber)
    {
        sceneStarting = false;
        StartCoroutine("EndSceneRoutine", SceneNumber);
    }
}   

LevelChanger.cs

using UnityEngine;
using System.Collections;

public class LevelChanger : MonoBehaviour {

    ScreenFader fadeScr;
    public int SceneNumb;

    void Awake()
    {
        fadeScr = GameObject.FindObjectOfType<ScreenFader>();
    }

    void OnTriggerEnter(Collider col)
    {
        if (col.gameObject.tag == "Player")
        {
            fadeScr.EndScene(SceneNumb);
        }
    }
}

hello, i'm trying to call the function EndScene(SceneNumb) from another script but it gives me an error ( NullReferenceException: Object reference not set to an instance of an object
StartMenu.StartLevel () (at Assets/Scripts/StartMenu.cs:130)
UnityEngine.Events.InvokableCall.Invoke (System.Object[] args) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:153)
UnityEngine.Events.InvokableCallList.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:630)
UnityEngine.Events.UnityEventBase.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:765)
UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:53)
UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:35)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:44)
UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:52)
UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler](UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:269)
UnityEngine.EventSystems.EventSystem:Update())

can you help me please ?

Awesome stuff! But I'm curious, why do you not disable the image after the fade is over, for efficiency's sake?