MovieClip(root) line seems to be crashing my game - actionscript-3

Question

Inside my classes, I invoke this function
MovieClip(root).increaseScore();
which handles the score in the main .as file.
It all works fine during the execution of the level. However when the level is finished and the screen goes to another frame, the game crashes and gives me this error
TypeError: Error #1009: Cannot access a property or method of a null
object reference.
on the line above.
How do I fix this?
Thanks
edit:
This is were I tell it to addScore, this is in the GameController.as file
private function removeBubble(bubble, addScore:Boolean)
{
var delay:Timer = new Timer(200, 1);
delay.addEventListener(TimerEvent.TIMER_COMPLETE, function(e:TimerEvent)
{
if(bubble.parent==mcGameStage)
{
var j:int = bubbleList.indexOf(bubble);
bubbleList.splice(j,1);
if(addScore) bubble.addScore();
mcGameUI.txtScorePlayer.text = String(playerScore);
mcGameStage.removeChild(bubble);
}
e.currentTarget.removeEventListener(e.type, arguments.callee);
checkWin();
});
delay.start();
}
here is the checkWin function:
private function checkWin()
{
if (playerBlue + playerRed + playerYellow + playerOrange + playerPurple + playerGreen == 0)
{
gameWin();
}
}
private function gameWin()
{
while (bubbleList.numChildren > 0)
{
bubbleList.removeChildAt(0);
}
mcGameUI.btnMixBlue.removeEventListener(MouseEvent.CLICK, mixBlue);
mcGameUI.btnMixRed.removeEventListener(MouseEvent.CLICK, mixRed);
mcGameUI.btnMixYellow.removeEventListener(MouseEvent.CLICK, mixYellow);
mcGameUI.btnNeedle.removeEventListener(MouseEvent.CLICK, activateNeedle);
mcGameStage.removeEventListener(Event.ENTER_FRAME,update);
mcGameStage.removeEventListener(MouseEvent.CLICK, checkToHit);
removeEventListener(Event.ADDED_TO_STAGE, gameAddedToStage );
stage.removeEventListener(KeyboardEvent.KEY_DOWN,keyDownHandler);
stage.removeEventListener(KeyboardEvent.KEY_UP,keyUpHandler);
if (mouseCursor != null)
{
mouseCursor.removeEventListener(Event.ENTER_FRAME,followMouse);
mouseCursor = null;
}
gotoAndPlay("level1win");
}
And inside my classes,
public function addScore()
{
root["increaseScore"]();
}
This is what increaseScore does
public function increaseScore()
{
playerScore += 1000;
}
So where is the null object? D:
Also I am very inexperienced using the debugger so I apologize if this could be easily solved with that. I tried it and couldn't figure it out before coming here.
What is OPP method?
What is FrameScript?
Also, the class is MovieClip
thanks :)

Answer 1

Fixing this is done with the help of the debugger!
The error is telling you that something is null and you're trying to access it. That's not good, so let's think what could be null?
1) Your movie clip instance might be null.
2) increaseScore() method of your movie clip instance might try to access something that is null
You didn't post any code that I could analyse at the time I'm writing this answer, so I can't say for sure.
Some possible problems:
Your class is not called MovieClip, but you're just trying to cast your root object to a MovieClip. Thing is, MovieClip's don't have a increaseScore() method. You should instead call the increaseScore() method with
root["increaseScore"]();
This will call the method of your root timeline, but since we are using weak-typing, you might have problems with debugging it later. But I guess that's the price you pay when writing all the code in a frame instead of using OPP approach.

Answer 2

The true reason here is said in the error: Cannot access a property or method of a null object reference.
What this means is that MovieClip(root) is null (it doesn't even bother to check if the function is present). The reasons for this might be three:
Your document class is not MovieClip (could be Sprite).
The class you use root in, is not DisplayObject. The property is part of the DislpayObject class and so if you use it on other kind of classes that does not extend it, it won't work.
You are using this piece of code before you have added the instance to the stage (most probable cause). The root property represents the top-most display object in the tree. If you haven't added the child to the tree, it has no roots :) Check out parent - the error should be the same.