php update

hi there
i have a entity (car) that have a pass property

but when i want to check if a property is null or player it only return one thing and never change it

i have this code for seat pas:

PHP:

public function seat_pass (Player $player){
if ($this->pass1 == null { // it say there is no passenger here
$this->pass1 = $player;
}
}

and get it:

PHP:

public function canAddPass (){
 if ($this->pass1 == null){
return true;
}
return false;
}

but it always return true and passenger add on there head :/
and i use

PHP:

public function onHit (){
//some code

if ($entity->canAddPass () === true){
//seat player
}
}

my entity extends to carBase that i made it and carBase extends Human entity

 

PHP:

protected $pass1;

 

but some of my cars will have 2 or 3 passengers what should i do for it?