Tidak menemukan error warning php yang dimaksut

saya mencoba mencari error berdasarkan warning phpnya dan dari video tutorialnya tapi tidak menemukan sumber error yang dimaksut, berdasarkan notif php errornya ada di baris 46, if($this->mysqli->query($query)) return true; tapi saya cek di video sudah sama codenya. video sekolahkoding 12 Sistem login dan register (OOP PHP) video 7

Fatal error: Uncaught Error: Call to a member function query() on null in C:\xampp\htdocs\belajarphp\auth\classes\database.php:46 Stack trace: #0 C:\xampp\htdocs\belajarphp\auth\classes\user.php(14): Database->insert('users', Array) #1 C:\xampp\htdocs\belajarphp\auth\register.php(9): User->register_user(Array) #2 {main} thrown in C:\xampp\htdocs\belajarphp\auth\classes\database.php on line 46

<?php
class Database{

    private  static $INSTANCE = null;
    private $mysqli,
            $HOST ='localhost',
            $USER = 'root',
            $PASS = '',
            $DBNAME = 'tutorial';
public function __construct(){
    $this->msqli = new mysqli($this->HOST, $this->USER, $this->PASS, $this->DBNAME);
    if(mysqli_connect_error()){
        die('gagal koneksinya');
    }
}
    // singleton pattern, menguji koneksi agar tidak double
    public static function getInstance(){
        if(!isset(self::$INSTANCE))
        {
            self::$INSTANCE= new Database();
        }
        return self::$INSTANCE;
    }

    public function insert($table, $fields = array())
    {     // mengambil kolom
        $column = implode(", ", array_keys($fields));

        // mengambil nilai
        $valueArrays = array();
        $i = 0;
        foreach($fields as $key=>$values){
            if(is_int($values)){
                $valueArrays[$i] = $values;
            }else {
                $valueArrays[$i] = "'" . $values . "'";
            }
            $i++;
        }
        $values = implode(", ", $valueArrays);

        $query = "INSERT INTO $table ($column) VALUES ($values)";

        if($this->mysqli->query($query)) return true;
        else return false;
    }
}
?>