Explicitly mark parameter as nullable

.github/workflows/unit-tests.yml

@@ -26,6 +26,7 @@ jobs:
           - "8.1"
           - "8.2"
           - "8.3"
+          - "8.4"
         operating-system:
           - "ubuntu-latest"
 

.php-cs-fixer.dist.php

@@ -41,6 +41,7 @@
         'strict_param' => true,
         'ternary_to_null_coalescing' => true,
         'native_function_invocation' => ['include' => ['@compiler_optimized'], 'scope' => 'namespaced'],
+        'nullable_type_declaration_for_default_null_value' => true,
     ])
     ->setFinder($finder)
 ;

src/DataCollector/MercureDataCollector.php

@@ -34,7 +34,7 @@ public function __construct(iterable $hubs)
         $this->hubs = $hubs;
     }
 
-    public function collect(Request $request, Response $response, \Throwable $exception = null): void
+    public function collect(Request $request, Response $response, ?\Throwable $exception = null): void
     {
         $this->data = [
             'count' => 0,