Mysql自动插入一个空行

Question

I am working with mysql in my project and when I try to call the webAPI to insert data to the database, it inserts an empty row before the inserted row.

Can anyone help please?

$rest_json = file_get_contents("php://input");
$_POST = json_decode($rest_json, true);

$nom = $_POST['nom'];

$query = "INSERT into class (nom_class) values('$nom')";
$result = $db->query($query);
if ($result === TRUE) {
    $res = "Inserted" . $nom;
    echo json_encode($res);
} else {
    echo json_encode("Error" . $query . "<br>" . $db->error);
}
break;

I have tried EMPTY, and ISSET features but it didn't work.

This is the database:

I'll be so grateful if any one could help.