class - AS3/Flash Builder - Cannot access a property of a null object reference -

this first time i've used flash builder (i use flash stuff). i've got bunch of non static classes , 1 of them has issue passing parameter constructor private var.

private function init():void {         var keys:primes = new primes();         var keyarray:array = [["kdc",keys.getrandomprime()],["client",keys.getrandomprime()],["server",keys.getrandomprime()]];         trace(keyarray);         kdc = new keydistcentre(keyarray);         client = new client(keyarray[1][1]);         server = new server(keyarray[2][1]); } 

it's kdc = new line causing issue, when pass keyarray it has problem assigning value private var in class.

package { public class keydistcentre extends client {     private var keylist:array = new array();      public function keydistcentre(keys:array)     {         super(keys[0][1]);          keylist = keys; **error**     }      public function generateticket():ticket     {          return null;     } } } 

the weird thing when comment out problematic lines, exact same error line reference occurs...