[4.x] Fix: Null header deprecated notice for PSR requests

src/Http/Faking/FakeResponse.php

@@ -124,7 +124,7 @@ public function createPsrResponse(ResponseFactoryInterface $responseFactory, Str
         $response = $responseFactory->createResponse($this->status());
 
         foreach ($this->headers()->all() as $headerName => $headerValue) {
-            $response = $response->withHeader($headerName, $headerValue);
+            $response = $response->withHeader($headerName, $headerValue ?? '');
         }
 
         return $response->withBody($this->body()->toStream($streamFactory));

src/Traits/PendingRequest/ManagesPsrRequests.php

@@ -48,7 +48,7 @@ public function createPsrRequest(): RequestInterface
         );
 
         foreach ($this->headers()->all() as $headerName => $headerValue) {
-            $request = $request->withHeader($headerName, $headerValue);
+            $request = $request->withHeader($headerName, $headerValue ?? '');
         }
 
         if ($this->body() instanceof BodyRepository) {

tests/Feature/PsrTest.php

@@ -5,6 +5,8 @@
 use GuzzleHttp\Psr7\Uri;
 use Saloon\Http\Faking\MockClient;
 use Saloon\Http\Faking\MockResponse;
+use Saloon\Tests\Fixtures\Connectors\TestConnector;
+use Saloon\Tests\Fixtures\Requests\NullHeaderRequest;
 use Saloon\Tests\Fixtures\Requests\ModifiedPsrUserRequest;
 use Saloon\Tests\Fixtures\Connectors\ModifiedPsrRequestConnector;
 
@@ -26,3 +28,20 @@
 
     expect($response->getPsrRequest()->getHeaders())->toHaveKey('X-Howdy', ['Yeehaw']);
 });
+
+test('The psr request headers must be converted to empty string', function () {
+    $mockClient = new MockClient([
+        MockResponse::make(headers: ['X-Null-Header' => null]),
+    ]);
+
+    $connector = new TestConnector();
+    $connector->withMockClient($mockClient);
+
+    $response = $connector->send(new NullHeaderRequest());
+
+    // The request will convert null to empty string
+    expect($response->getPsrRequest()->getHeader('X-Null-Header')[0])->toBe('');
+
+    // The response will convert null header to empty string
+    expect($response->headers()->get('X-Null-Header'))->toBe('');
+});

tests/Fixtures/Requests/NullHeaderRequest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Saloon\Tests\Fixtures\Requests;
+
+use Saloon\Enums\Method;
+use Saloon\Http\Request;
+
+class NullHeaderRequest extends Request
+{
+    /**
+     * Define the method that the request will use.
+     *
+     * @var string
+     */
+    protected Method $method = Method::GET;
+
+    /**
+     * Define the endpoint for the request.
+     */
+    public function resolveEndpoint(): string
+    {
+        return '/user';
+    }
+
+    protected function defaultHeaders(): array
+    {
+        return [
+            'X-Null-Header' => null,
+        ];
+    }
+}