MYSQL Query не может получить данные из базы данных

Проблема в том, что мой запрос:

SELECT * FROM administradores WHERE nombre_administrador=? AND password=?

ничего не вытаскивает из базы данных.

var_dump показывает:

  public 'affected_rows' => null, public 'insert_id' => null
public 'num_rows' => null
public 'param_count' => null
public 'field_count' => null
public 'errno' => null
public 'error' => null
public 'error_list' => null
public 'sqlstate' => null
public 'id' => null

login.php

<?php
class login{
//Variable for MySql connection
private $hookup;
private $sql;
private $tableMaster;

//Field Variables
private $pass;
private $name;

public function __construct()
{
//Get table name and make connection
$this->mysqli=UniversalConnect::doConnect();

//Get data from HTML form
$this->name=$_POST['name'];
$this->pass=$_POST['pass'];
//Call private methods for MySql operations
$this->dologin();
$this->mysqli->close();
}

private function dologin()
{
if ($stmt = $this->mysqli->prepare("SELECT * FROM administradores WHERE nombre_administrador=? AND password=?")){
var_dump($stmt);
/* bind parameters for markers */
$stmt->bind_param('ss', $this->name, $this->pass);
var_dump($this->name);
var_dump($this->pass);
/* execute query */
$stmt->execute();

/* bind result variables */
$stmt->bind_result($id,$nombre_administrador,$password,$ubicacion,$nombre,$apellido);

/* fetch value */
$stmt->fetch();
/*get number of rows*/
$num_row =$stmt->num_rows;

if($num_row==1){
echo 'true';
$_SESSION['Name'] = $row['nombre_administrador'];
$_SESSION['Id'] = $row['id'];
header("location:  http://localhost/SCAF1.0/indexSCAF.html");
} else {
echo "<script>alert('wrong password');</script>";
echo 'false';
}
} else{
echo "Falló la conexión con MySQL: (" . $this->mysqli->connect_errno . ") " . $this->mysqli->connect_error;
}

$stmt->close();
}
}
?>