Error calling property or method

Hello! Wrote the code for the quiz. Everything works, questions are asked randomly, but at some point the application stops and the following error is displayed: "TypeError: Error # 1009: Cannot call a property or method with reference to the object" null ".at Main / asking () at Main / onClick ( ) ". I tried to eliminate it, applied tracing, but did not find a bug. In addition, an error occurs every time in a new place: it may appear after the first question, or after the tenth or any other. I fight the second day, I did not find the answer in the search engine. Here is the code itself:

package { import flash.display.*; import flash.events.*; import flash.net.*; import flash.text.*; import TfFormat; public class Main extends Sprite { var externalXML:XML;//загруженный XML var numOfQuestion:Number;//число вопросов var currentXML:XML=new XML;//XML текущего вопрсоа var currentElementText:String='';//текущий вариант ответа var i;// номер текущего вопроса var massiv:Array=[];// массив с ответами var loader:URLLoader = new URLLoader(); var request:URLRequest=new URLRequest("super.xml"); var textF:TfFormat = new TfFormat; var rnd:RND; //экземпляр генератора номера вопроса public function Main() { loader.load(request); loader.addEventListener(Event.COMPLETE, preOnComplete); } /* Функция загрузки XML-файла */ function preOnComplete(event:Event):void { var tf:TextField = new TextField; tf.text = 'Викторина' tf.setTextFormat(textF); var goStart:AnswerBut = new AnswerBut('запуск викторины'); tf.x =30; tf.y =30; tf.width = 300; tf.height = 40; goStart.x = 50; goStart.y = 50; addChild(tf); addChild(goStart); goStart.addEventListener(MouseEvent.CLICK, onComplete); } function onComplete(event:Event):void { if (this.numChildren>1) { while (this.numChildren > 1) { this.removeChildAt(1); } } if (loader!=null) { externalXML=new XML(loader.data); numOfQuestion = externalXML.quest.length(); asking(externalXML.quest.length()+1); //запускаем первый вопрос } } 

The function asking (numOff) is responsible for the task process of a specific question. The parameter of the function is passed the number of the previous question, which should not be set again. When you first start the function, this number is longer than the length of the array of questions. /

  function asking(numOff):void { var currentRandom:Number = numOff; //присваиваем текущему номеру //вопроса предыдущий номер вопроса while(currentRandom == numOff) { currentRandom = Math.round(Math.random()*numOfQuestion); //создаем номер вопроса, не равный //предыдущему номеру } currentXML=externalXML.quest[currentRandom]; //текущий вопрос в виде XML var tf:TextField = new TextField; tf.text = currentXML.@text.toString(); tf.setTextFormat(textF); tf.width = 400; tf.height = 40; tf.x = 20; tf.y = 70; tf.wordWrap = true; addChild(tf); var numMassiv:Array = []; for (var i=0; i<currentXML.answer.length(); i++) { numMassiv[i] = i } var answerMassiv:Array = []; var answerNum = numMassiv.length; for (var k=0; k<answerNum; k++) { var kk = Math.round(Math.random()*(numMassiv.length-1)); answerMassiv[k]=new AnswerBut(currentXML.answer[numMassiv[kk]]); if (numMassiv[kk] == 0) answerMassiv[k].correct = true; answerMassiv[k].num = currentRandom; trace(currentRandom); numMassiv.splice(kk,1); answerMassiv[k].x=30; answerMassiv[k].y=k*20+120; addChild(answerMassiv[k]); answerMassiv[k].addEventListener(MouseEvent.CLICK, onClick); } } function onClick(e:MouseEvent):void { var prev = new Number(e.target.num); //удаляем всех потомков класса if (this.numChildren>1) { while (this.numChildren > 1) { this.removeChildAt(1); } } asking(prev); } } 

}