actionscript 3 - AS3 - How do you Ignore a class (Error #1009)? -

i have created class movieclip creating coins player (char) pick up. class suppose add score , coinscollected variables, , remove 1 coin stage. when change frame using gotoandstop(#);, console spams

errortype: error #1009: cannot access property or method of null object reference."

coin class:

public class coin extends movieclip{     var char:movieclip;     var maintimeline = movieclip(root);     public function coin() {         // constructor code             this.addeventlistener(event.enter_frame,update);      }      function update(event:event):void{         if(maintimeline.currentframe!=5){             char=movieclip(root).char;             if(this.hittestobject(char)){                 this.removeeventlistener(event.enter_frame,update);                 parent.removechild(this);                 maintimeline.score++;                 maintimeline.coinscollected++;             }         }     }  } 

root isn't populated until display object has been added display list. need listen event before setting variable.

var char:movieclip; var maintimeline; //do not initialize here, root null @ point  public function coin() {     // constructor code      //root still null here too, see if it's populated yet     if(root){         init(); //root populated, skip initialization     }else{         this.addeventlistener(event.added_to_stage,addedtostage);  //root isn't populated yet, listen added stage , initialize     } }  private function addedtostage(e:event = null):void {     this.removeeventlistener(event.added_to_stage,addedtostage);     init(); }  private function init():void {     maintimeline = movieclip(root)     this.addeventlistener(event.enter_frame,update); } 

---