php ftp检查文件夹是否存在总是返回错误创建文件夹

$ftp_server = "ftp.example.com";
$ftp_username = "username";
$ftp_password = "password";

$conn_id = ftp_connect($ftp_server) or die("Could not connect to $ftp_server");
$login_result = ftp_login($conn_id, $ftp_username, $ftp_password);

if (ftp_nlist($conn_id, "/path/to/folder") != false) {
    echo "文件夹存在";
} else {
    ftp_mkdir($conn_id, "/path/to/folder");
    echo "文件夹已创建";
}

ftp_close($conn_id);

$ftp_server = "ftp.example.com";
$ftp_username = "username";
$ftp_password = "password";

$conn_id = ftp_connect($ftp_server) or die("Could not connect to $ftp_server");
$login_result = ftp_login($conn_id, $ftp_username, $ftp_password);

if (@ftp_chdir($conn_id, "/path/to/folder")) {
    echo "文件夹存在";
} else {
    ftp_mkdir($conn_id, "/path/to/folder");
    echo "文件夹已创建";
}

ftp_close($conn_id);