Hi Please any one can help with solution, i am getting following error,  while writing controller "System.LimitException: Maximum stack depth reached: 1001 ". And this is my controller. May I know what is the Error, why I am getting this erroe and in which cases I am getting this type of error.

public with sharing class jkk_save1_controller {

public contact acc{get;set;}
public jkk_save1_controller(){
acc=new contact();
}

public PageReference savecon() {
return null;
}
}