mailgun-php: Uncaught InvalidArgumentException: First argument to "Http\Message\MultipartStream\MultipartStreamBuilder::createStream()" must be a string, resource or StreamInterface

<?php

declare(strict_types=1);

require_once './vendor/autoload.php';

use Mailgun\Mailgun;

define("API_KEY", "");
define("API_DOMAIN", "");
define("SUBLIST", "");
define("EMAIL", "");

$mailgun = Mailgun::create(API_KEY);
$mailgun->mailingList()->member()->create(
    SUBLIST,
    EMAIL,
    null, // name
    [],
    false,
    true
);

$parameters = [
    'name' => null, // name
    'subscribed' => 'yes',
];

$mailgun->mailingList()->member()->update(
    SUBLIST,
    EMAIL,
    $parameters
);

Null name will cause error:

PHP Fatal error: Uncaught InvalidArgumentException: First argument to “Http\Message\MultipartStream\MultipartStreamBuilder::createStream()” must be a string, resource or StreamInterface. in /home/zolotukhin/Projects/github/test-mailgun/vendor/php-http/multipart-stream-builder/src/MultipartStreamBuilder.php:332