quest.visible=true;
com7.visible=false;
quest.addEventListener(MouseEvent.CLICK, q7_clicked);
function q7_clicked(event:MouseEvent):void
{

    if  (com7.visible==false)
    {com7.visible=true
    }
    else
    {
    com7.visible=false;
    }
    }

quest.visible=true;

com9.visible=false;
quest.addEventListener(MouseEvent.CLICK, q9_clicked);

function q9_clicked(event:MouseEvent):void
{

    if  (com9.visible==false)
    {com9.visible=true
    }
    else
    {
    com9.visible=false;
    }
    }

TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at meli_fla::MainTimeline/q7_clicked()
TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at meli_fla::MainTimeline/q9_clicked()