Undefined property из-за чего?

require_once("engine/DB.php");
$db = new DB("", "", "", "");

require_once("engine/functions.php");
$func = new Functions();

$func->auth("login", "pass");

class DB
{
	private $link;
	
	public function __construct($hostname, $username, $password, $database, $port = 3306)
	{
		$this->link = new mysqli($hostname, $username, $password, $database, $port);
		
		if($this->link->connect_error)
		{
	  		exit("Ошибка: Не удалось соединиться с сервером базы данных!");
		}
		
		$this->link->query("SET NAMES 'utf8'");
		$this->link->query("SET CHARACTER SET utf8");
		$this->link->query("SET CHARACTER_SET_CONNECTION=utf8");
		$this->link->query("SET SQL_MODE = ''");
  	}
	
  	public function query($sql)
	{
		if(!$resource = $this->link->query($sql))
		{
			exit("Error: " . $this->link->error . " (#" . $this->link->errno . ")" . "<br>" . $sql);
		}
		
		if(is_object($resource))
		{
			$i = 0;
			$data = array();
			
			while($row = $resource->fetch_assoc())
			{
				$data[$i] = $row;
				$i++;
			}
			
			$resource->free();
			
			$query = new stdClass();
			$query->row = isset($data[0]) ? $data[0] : array();
			$query->rows = $data;
			$query->num_rows = $i;
			
			unset($data);
			return $query;
		}
  	}
	
	public function escape($value)
	{
		return $this->link->real_escape_string($value);
	}
	
  	public function getLastId()
	{
		return $this->link->insert_id;
  	}
	
	public function __destruct()
	{
		return $this->link->close();
	}
}