如果找不到类中的属性，如何在函数/方法内返回null？

I use stdClass to convert an array to an object,

function array_to_object($array)
{
    if(!is_array($array)) {
        return $array;
    }

    $object = new stdClass();
    foreach($array as $key => $value)
    {
        $key = (string) $key ;
        $object->$key = is_array($value) ? array_to_object($value) : $value;
    }

    return $object;
}

$type = array(
    "category"  => "admin",
    "person"    => "unique"
);

$type = array_to_object($type);

var_dump($type->category); // string(5) "admin" 

and of course an error when I want to get the property which is not set in the array in the first place,

var_dump($type->image);

error message,

Notice: Undefined property: stdClass::$image in C:\wamp\www\test\2012\php\array_to_object.php on line 52
NULL

I wonder if I can make the function to return null if no property is found?

 var_dump($type->image); //NULL

EDIT:

Decided to make that function above into a class, but still cannot get __get() working properly,

class objectify
{
    public function __get($name)
    {
        if (isset($this->$name) === true){
            return $this->$name;
        } else {
            return null;
        }
    }

    public function array_to_object($array)
    {
        if(!is_array($array)) {
            return $array;
        }

        $object = self::__get($name);
        foreach($array as $key => $value)
        {
            $key = (string) $key ;
            $object->$key = is_array($value) ? self::array_to_object($value) : $value;
        }
        return $object;
    }
}


$object = new objectify();

$type = array(
    "category"  => "admin",
    "person"    => "unique"
);

$type = $object->array_to_object($type);
var_dump($type->category);
var_dump($type->image);

error message,

Notice: Undefined variable: name in C:\wamp\www\test\2012\php\array_to_object.php on line 85
string(5) "admin" 
Notice: Undefined property: stdClass::$image in C:\wamp\www\test\2012\php\array_to_object.php on line 107
NULL

I think this line is where the error from but I don't know what to do with it...

$object = self::__get($name);

Bringing John's answer about __get() together:

<? //PHP 5.3+

class maybeBag {
    public function __get($name){
        if (isset($this->$name) === true){
            return $this->$name;
        } else {
            return null;
        }
    }

    public static function ensureIsObject($values){
        if (\is_array($values) !== true){
            return $values;
        }
        $o = new static(); //Late-bound make instance of own class
        foreach($values as $key => $value){
            $o->$key = static::ensureIsObject($value);
        }
        return $o;
    }
}

//Demo

$type = array(
    'category' => 'admin',
    'person'   => 'unique'
);
$type = maybeBag::ensureIsObject($type);

var_dump($type->category); //string(5) "admin"
var_dump($type->image); //NULL

?>

Untested, but I think using the magic method __get() might work here:

public function __get($parameter)
{
    return (isset($this->$parameter)) ? $this->$parameter : null;
}

Use this magic method inside your class. Whenever an undefined property is requested, null is returned.

For PHP 7:

public function __get($prop){
    return $this->$prop ?? null;
}

For PHP 5:

public function __get($prop){
    return isset($this->$prop) ? $this->$prop: null;
}