Cannot access a property or method of a null object reference. -enterframe.Trying to get palayer out of maze - actionscript-3

Question

i'm making a simple game and i'm still learning as3 i want to hit test object on the stage , player with box if hittestobject gotoframe or scene all the objects are on the stage with corect instancename, maintimeline as3 below everything works fine but i get the null error.
it is a maze game.
import flash.events.KeyboardEvent;
import flash.events.Event;
import flash.geom.Rectangle;
import flash.ui.Keyboard;
var rightArrow:Boolean = false;
var leftArrow:Boolean = false;
var upArrow:Boolean = false;
var downArrow:Boolean = false;
var speed:int = 20;
stage.addEventListener(KeyboardEvent.KEY_DOWN, stage_onKeyDown);
stage.addEventListener(KeyboardEvent.KEY_UP, stage_onKeyUp);
stage.addEventListener(Event.ENTER_FRAME, stage_onEnterFrame);
function stage_onKeyDown(event:KeyboardEvent):void {
if(event.keyCode == Keyboard.RIGHT) rightArrow = true;
if(event.keyCode == Keyboard.LEFT) leftArrow = true;
if(event.keyCode == Keyboard.UP) upArrow = true;
if(event.keyCode == Keyboard.DOWN) downArrow = true;
}
function stage_onKeyUp(event:KeyboardEvent):void {
if(event.keyCode == Keyboard.RIGHT) rightArrow = false;
if(event.keyCode == Keyboard.LEFT) leftArrow = false;
if(event.keyCode == Keyboard.UP) upArrow = false;
if(event.keyCode == Keyboard.DOWN) downArrow = false;
}
function stage_onEnterFrame(event:Event):void {
var rect:Rectangle = player.getBounds(this);
var i:int = 0;
var xBump:int = 0;
var yBump:int = 0;
if(rightArrow) {
xBump = speed;
for(i = 0; i < speed; i++) {
if(maze.hitTestPoint(rect.right + i, player.y, true)) {
xBump = i - 1;
break;
}
}
}
if(player.hitTestObject(box))
{
// Go to next scene
nextFrame();
}
if(leftArrow) {
xBump = -speed;
for(i = 0; i < speed; i++) {
if(maze.hitTestPoint(rect.left - i, player.y, true)) {
xBump = -i + 1;
break;
}
}
}
if(upArrow) {
yBump = -speed;
for(i = 0; i < speed; i++) {
if(maze.hitTestPoint(player.x, rect.top - i, true)) {
yBump = -i + 1;
break;
}
}
}
if(downArrow) {
yBump = speed;
for(i = 0; i < speed; i++) {
if(maze.hitTestPoint(player.x, rect.bottom + i, true)) {
yBump = i - 1;
break;
}
}
}
player.x += xBump;
player.y += yBump;
}