PHP interface optional parameter

     

I'm trying to make an generic interface for my service classes. I'm having trouble with a two class making use of the interface. They share a methode called create. The create methode excepts three parameters. I want it to make it so that the third parameter is optional so that both classes can work with it.


interface ServiceInterface{
public static function create($var1 $var2 $thisOneIsOptional);
}
class ServiceObject1 implements ServiceInterface{
public static function create($url