TypeError: Error #1009: Cannot access a property or method of a null object reference. at Sound_fla::MainTimeline/goReturn()

The situation is the page will go back when the music starts. But if the music is not on, the error comes out and it will not go back. This is my action script for the page:

import flash.media.Sound;

import flash.net.URLRequest;

import flash.media.SoundChannel;

import flash.events.MouseEvent;

var my_songs:XMLList;

var my_total:Number;

var my_sound:Sound;

var my_channel:SoundChannel;

var current_song:Number = 0;

var song_position:Number;

var song_paused:Boolean;

var myXMLLoader:URLLoader = new URLLoader();

myXMLLoader.load(new URLRequest("playlist.xml"))

myXMLLoader.addEventListener(Event.COMPLETE, processXML);

function processXML (event:Event):void{

  var myXML:XML = new XML(event.target.data);

my_songs = myXML.SONG;

my_total = my_songs.length();

myXMLLoader.removeEventListener(Event.COMPLETE, processXML);

myXMLLoader = null;

}

function playSong(mySong:Number):void{

  var myTitle = my_songs[mySong].@TITLE;

  var myArtist = my_songs[mySong].@ARTIST;

  var myURL = my_songs[mySong].@URL;

title_txt.text = myTitle;

artist_txt.text = myArtist;

if (my_channel){

  my_channel.stop();

  my_channel.removeEventListener(Event.SOUND_COMPLETE, nextSound);

}

my_sound = new Sound();

my_sound.load(new URLRequest(myURL));

my_channel = my_sound.play();

my_channel.addEventListener(Event.SOUND_COMPLETE, nextSound);

}

nextBtn.addEventListener(MouseEvent.CLICK, nextSound);

function nextSound(event:Event):void{

  current_song++;

  if (current_song>=my_total){

  current_song=0;

  }

  playSong(current_song);

}

prevBtn.addEventListener(MouseEvent.CLICK, prevSound);

function prevSound(event:MouseEvent):void{

  current_song--;

  if (current_song<0){

  current_song = my_total-1;

  }

  playSong(current_song);

}

pauseBtn.addEventListener(MouseEvent.CLICK, pauseSound);

function pauseSound(event:MouseEvent):void{

  if (my_channel){

  song_position = my_channel.position;

  my_channel.stop();

  song_paused=true;

  }

}

playBtn.addEventListener(MouseEvent.CLICK, playSound);

function playSound(event:MouseEvent):void{

  if (song_paused){

  my_channel = my_sound.play(song_position);

  song_paused=false;

  } else if (!my_channel){

  playSong(current_song);

  }

}

backBtn.addEventListener(MouseEvent.CLICK, goReturn)

function goReturn (event:MouseEvent):void{

  my_channel.stop();

  var request:URLRequest = new URLRequest("Home.swf");

  var myLoader:Loader = new Loader();

  myLoader.load(request);

  addChild(myLoader);

}