Problems using OnLevelWasLoaded()

Hello, I am currently working on two aspects of my game in unity regarding the scripting for the main menu before the game is played. I am trying to make the scene change while simultaneously keeping the music going and to also have the scenes fade in and out. I am getting an error though regarding the "OnLevelWasLoaded" in both of my MusicPlayer and Fading scripts as a warning and I am getting an error for those same methods in my musicplayer script every times the scene changes. It mentions that "object reference not set to an instance of an object". I am am not sure what is causing these errors and was wondering if someone could see my error... Here is my fading script:

     using UnityEngine;
     using System.Collections;
     
     public class Fading : MonoBehaviour {
     
         public Texture2D fadeOutTexture;    // the texture that will overlay the screen. This can be a black image or a loading graphic
         public float fadeSpeed = 0.8f;        // the fading speed
     
         private int drawDepth = -1000;        // the texture's order in the draw hierarchy: a low number means it renders on top
         private float alpha = 1.0f;            // the texture's alpha value between 0 and 1
         private int fadeDir = -1;            // the direction to fade: in = -1 or out = 1
     
         void OnGUI()
         {
             // fade out/in the alpha value using a direction, a speed and Time.deltaTime to convert the operation to seconds
             alpha += fadeDir * fadeSpeed * Time.deltaTime;
             // force (clamp) the number to be between 0 and 1 because GUI.color uses Alpha values between 0 and 1
             alpha = Mathf.Clamp01(alpha);
     
             // set color of our GUI (in this case our texture). All color values remain the same & the Alpha is set to the alpha variable
             GUI.color = new Color (GUI.color.r, GUI.color.g, GUI.color.b, alpha);
             GUI.depth = drawDepth;                                                                // make the black texture render on top (drawn last)
             GUI.DrawTexture(new Rect(0, 0, Screen.width, Screen.height), fadeOutTexture);        // draw the texture to fit the entire screen area
         }
     
         // sets fadeDir to the direction parameter making the scene fade in if -1 and out if 1
         public float BeginFade (int direction)
         {
             fadeDir = direction;
             return (fadeSpeed);
         }
     
         // OnLevelWasLoaded is called when a level is loaded. It takes loaded level index (int) as a parameter so you can limit the fade in to certain scenes.
         void OnLevelWasLoaded()
         {
             // alpha = 1;        // use this if the alpha is not set to 1 by default
             BeginFade(-1);        // call the fade in function
         }
     }

the music player script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class MusicPlayer : MonoBehaviour {
 
     private float currentMusicTime;
     private AudioSource ad;
  
     void Start()
     {
         DontDestroyOnLoad(gameObject);
         ad = GameObject.Find("Music Holder").GetComponent<AudioSource>();
     }
 
     void Update()
     {
         currentMusicTime = ad.time;
         if (currentMusicTime == 0)
         {
             ad.Play();
         }
         
     }
 
     void OnLevelWasLoaded()
     {
         ad.time = currentMusicTime;
     }
 
 
 }
 

and the script to change scenes:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
 
 public class Scene : MonoBehaviour {
 
     public string ChangeToScene;
 
     public void ChangeScene(){
         float fadeTime = GameObject.Find ("Canvas").GetComponent<Fading> ().BeginFade (1);
         //yield return new WaitForSeconds (fadeTime);
         SceneManager.LoadScene (ChangeToScene);
     }
    
 }