Response laravel 4.2 shows key:value and index:value from DB query

Question

I have code like this

$idUser = Input::get('idUser');
$user = User::where('id', $idUser)
        ->first();

return Response::json($user, 200, [], JSON_NUMERIC_CHECK);

and shows as following

{
    "id": 22941,
    "0": 22941,
    "name": "Thanos",
    "1": "Thanos",
    "lastname": "El titan",
    "2": "El titan"
}

This only happens in local enviroment. I don't know if I have to change any config or what am I doing wrong. Thanks