mysql fetch（）返回null值

I'm really new to php, I wanted to get data that has been stored before using fetch(). It return the exact number of rows in the database, but with null values.

ini_set('display_errors', 1);

require_once 'DbOperation.php';

$db = new DbOperation(); 

$devices = $db->getAllDevices();

$response = array(); 

$response['error'] = false; 
$response['antrian_mobile'] = array(); 

while($device = $devices->fetch()){
    $temp = array();
    $temp['id']=$device['id'];
    $temp['email']=$device['email'];
    $temp['token']=$device['token'];
    array_push($response['antrian_mobile'],$temp);
}

echo json_encode($response);

the function of getAllDevices:

public function getAllDevices(){
    $stmt = $this->con->prepare(" SELECT email, token FROM antrian_mobile ");
    //$stmt->bind_param("s",$email);
    $stmt->bind_result($email,$token);
    $stmt->execute();
    //$stmt->store_result();
    //$result = $stmt->get_result();
    return $stmt; 
}

what is wrong with this code?

Hello i think you had return wrong value into getAllDevices function.

remove the comment from this "$result = $stmt->get_result()".

and return the $result variable instead of $stmt.

try this