I am using XML to load the slider.as but when I click on the next button I get this Error , What does that mean?

Error #1009: Cannot access a property or method of a null object reference.

at com::slider/fn_show_notice()

I am getting this Error when I am at case 9

I have the Function as below :

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  private function fn_show_notice(IN_Event:MouseEvent):void
  {
   //trace("show notice");
  
   btn_showNotice.visible         = false;
  
   if(mc_notice != null)
   {
   
    return;
   
   }
  
   switch(int_counter)
   {
    case 9:
   
     mc_notice         = new com.popup1();
    
     mc_notice.txt_heading.text     = xml_popup.popup[0].heading;
    
     mc_notice.txt_data.htmlText    = xml_popup.popup[0].text;

     break;  
    
    
    case 13:
   
     mc_notice         = new com.popup1();
    
     mc_notice.txt_heading.text     = xml_popup.popup[1].heading;
    
     mc_notice.txt_data.htmlText    = xml_popup.popup[1].text;

     break;
    
    case 17:
   
     mc_notice         = new com.popup1();
    
     mc_notice.txt_heading.text     = xml_popup.popup[4].heading;
    
     mc_notice.txt_data.htmlText    = xml_popup.popup[4].text;

     break;  
    
    case 22:
   
     mc_notice         = new com.popup1();
    
     mc_notice.txt_heading.text     = xml_popup.popup[5].heading;
    
     mc_notice.txt_data.htmlText    = xml_popup.popup[5].text;

     break;  
    
    case 23:
   
     mc_notice         = new com.popup1();
    
     mc_notice.txt_heading.text     = xml_popup.popup[6].heading;
    
     mc_notice.txt_data.htmlText    = xml_popup.popup[6].text;

     break; 
    
    case 35:
   
     mc_notice         = new com.popup1();
    
     mc_notice.txt_heading.text     = xml_popup.popup[6].heading;
    
     mc_notice.txt_data.htmlText    = xml_popup.popup[6].text;

     break; 
    
    case 36:
   
     mc_notice         = new com.popup1();
    
     mc_notice.txt_heading.text     = xml_popup.popup[6].heading;
    
     mc_notice.txt_data.htmlText    = xml_popup.popup[6].text;

     break;      

   }

   mc_notice.x          = 44.95;
  
   mc_notice.y          = 69;

   addChild(mc_notice);
  }