PHP Fatal error on the MultipartStream with PumpStream instance

[James ZHANG]

PHP version: 7.4.24

Description

Here's a case about the MultipartStream usage. If I want to compose the multipart instance with the PumpStream instance, A PHP Fatal error on there. The problem maybe on the following line:

https://github.com/guzzle/psr7/blob/master/src/MultipartStream.php#L92

PHP Fatal error:  Uncaught TypeError: substr() expects parameter 1 to be string, null given in /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php:92
Stack trace:
#0 /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php(92): substr(NULL, 0, 6)
#1 /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php(71): GuzzleHttp\Psr7\MultipartStream->addElement(Object(GuzzleHttp\Psr7\AppendStream), Array)
#2 /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php(35): GuzzleHttp\Psr7\MultipartStream->createStream(Array)
#3 /dummytest/test-multipart.php(17): GuzzleHttp\Psr7\MultipartStream->__construct(Array)
#4 {main}
  thrown in /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php on line 92

Fatal error: Uncaught TypeError: substr() expects parameter 1 to be string, null given in /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php:92
Stack trace:
#0 /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php(92): substr(NULL, 0, 6)
#1 /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php(71): GuzzleHttp\Psr7\MultipartStream->addElement(Object(GuzzleHttp\Psr7\AppendStream), Array)
#2 /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php(35): GuzzleHttp\Psr7\MultipartStream->createStream(Array)
#3 /dummytest/test-multipart.php(17): GuzzleHttp\Psr7\MultipartStream->__construct(Array)
#4 {main}
  thrown in /dummytest/vendor/guzzlehttp/psr7/src/MultipartStream.php on line 92

How to reproduce

<?php
require_once('./vendor/autoload.php');

use GuzzleHttp\Psr7\Utils;
use GuzzleHttp\Psr7\MultipartStream;

$buf1 = Utils::streamFor('dummy text1.');
$buf2 = Utils::streamFor(static function() { return 'dummy text2.'; });

$stream = new MultipartStream([
    [
        'name' => 'test1',
        'contents' => $buf1,
    ],
    [
        'name' => 'test2',
        'contents' => $buf2,
    ],
]);

print_r($stream);

Possible Solution

The getMetadata method should returns null while there wasn't the uri meta data available.
On L92, here should be checked that the $uri is Truthy then call substr function.