Adobe Animate CC dynamic text null error - actionscript-3

Question

I have got this error
"TypeError: Error #1009: Cannot access a property or method of a null object reference.
at sole_fla::MainTimeline/game()"
I just can't seems to display my score on the dynamic text box that I created that I named as "scoretext"
this is my code
import flash.events.Event;
import flash.events.KeyboardEvent;
import flash.ui.Keyboard;
import flash.display.MovieClip;
addEventListener(Event.ENTER_FRAME, game);
addEventListener(MouseEvent.CLICK, onClick);
var score:int = 0;
var high:int = 0;
const gravity:Number = 2;
const force: Number = 30;
const lyfe: Number = 100;
var yspeed: Number = 249;
var life: Number = 0;
function onClick(event:MouseEvent):void
{
//just testing if mouse input is detected
trace("The event handler works!");
}
//game main loop
function game(event: Event) {
score = 0;
life = lyfe;
yspeed = yspeed + gravity;
player.y = yspeed;
if(player.y - player.height/2 < 0)
player.y = player.height/2;
for (var i = 0; i < numChildren; i++) {
//test if mons hit player
if (mons.hitTestObject(player)){
life = life - 10;
trace("hit");
}
//test if starz hit player
if (starz.hitTestObject(player)){
//I believe this is the part where it gets the error
//this is my scoretext dynamic text box to display the score
scoretext.text = score.toString();
++score;
}
}
}
stage.addEventListener(KeyboardEvent.KEY_DOWN, fl_KeyboardDownHandler_2);
function fl_KeyboardDownHandler_2(event:KeyboardEvent):void
{
if(event.keyCode == 32){
yspeed = yspeed - force;
trace("Key Code Pressed: " + event.keyCode);
player.gotoAndPlay(41);
}
}

Answer 1

Changing frames does not go together well with persistent event listeners.
The listener is executed, but references to objects are null if the object is not present on the current frame.
When switching states in your application, terminate previous states properly by removing event listeners.