diff --git a/src/actions/RenderCompiledClasses.php b/src/actions/RenderCompiledClasses.php
index 0ecc7ba..0844624 100644
--- a/src/actions/RenderCompiledClasses.php
+++ b/src/actions/RenderCompiledClasses.php
@@ -53,7 +53,7 @@ protected function render(bool $forceRecreate)
         file_put_contents($compiledClassPath, $compiledClass);
     }
 
-    protected function cleanupOldMixins(string $except = null)
+    protected function cleanupOldMixins(?string $except = null)
     {
         $compiledClassesPath = __DIR__.'/../storage/';
 
diff --git a/src/behaviors/TestableResponseBehavior.php b/src/behaviors/TestableResponseBehavior.php
index 6e33bdf..97e2c87 100644
--- a/src/behaviors/TestableResponseBehavior.php
+++ b/src/behaviors/TestableResponseBehavior.php
@@ -181,7 +181,7 @@ public function querySelector(string $selector)
      *
      * To submit the form use `->submit()` or `->click('.button-selector')`.
      */
-    public function form(string $selector = null): Form
+    public function form(?string $selector = null): Form
     {
         if ($selector === null) {
             if ($this->form) {
@@ -240,7 +240,7 @@ public function assertCacheTag(string ...$tags)
      * $response->assertCookie('cookieName', 'cookie value'); // checks that the values match
      * ```
      */
-    public function assertCookie(string $name, string $value = null)
+    public function assertCookie(string $name, ?string $value = null)
     {
         if ($value === null) {
             Assert::assertContains($name, array_keys($this->response->cookies->toArray()));
@@ -360,7 +360,7 @@ public function assertDontSeeText(string $text)
      * $response->assertDownload('file.jpg'); // checks that a download with the name `file.jpg` is returned
      * ```
      */
-    public function assertDownload(string $filename = null)
+    public function assertDownload(?string $filename = null)
     {
         $contentDisposition = explode(';', $this->response->headers->get('content-disposition'));
 
@@ -438,7 +438,7 @@ public function assertForbidden()
      * $response->assertHeader('x-foo', 'bar'); // checks for header with matching value
      * ```
      */
-    public function assertHeader(string $name, string $expected = null)
+    public function assertHeader(string $name, ?string $expected = null)
     {
         if ($expected === null) {
             Assert::assertContains($name, array_keys($this->response->headers->toArray()));
@@ -488,7 +488,7 @@ public function assertJson(array|callable $value, $strict = false)
         return $this->response;
     }
 
-    public function assertJsonCount(int $count, string $key = null)
+    public function assertJsonCount(int $count, ?string $key = null)
     {
         $this->getJsonContent()->assertCount($count, $key);
 
@@ -535,7 +535,7 @@ public function assertJsonMissingPath(string $path)
         return $this->response;
     }
 
-    public function assertJsonStructure(array $structure = null, $responseData = null)
+    public function assertJsonStructure(?array $structure = null, $responseData = null)
     {
         $this->getJsonContent()->assertStructure($structure, $responseData);
 
@@ -564,7 +564,7 @@ public function assertJsonValidationErrors()
      * $response->assertLocation('/foo', ['host', 'path']);
      * ```
      */
-    public function assertLocation(string $location, array $checkParts = null)
+    public function assertLocation(string $location, ?array $checkParts = null)
     {
         $header = $this->response->getHeaders()->get('Location');
         $headerParts = parse_url($header);
@@ -612,7 +612,7 @@ public function assertLocationPath(string $uri)
      * $response->assertFlash('Field is required', 'title');
      * ```
      */
-    public function assertFlash(string $message = null, string $key = null)
+    public function assertFlash(?string $message = null, ?string $key = null)
     {
         $flash = \Craft::$app->getSession()->getAllFlashes();
 
diff --git a/src/craft/services/ProjectConfig.php b/src/craft/services/ProjectConfig.php
index be07e96..8985b11 100644
--- a/src/craft/services/ProjectConfig.php
+++ b/src/craft/services/ProjectConfig.php
@@ -4,7 +4,7 @@
 
 class ProjectConfig extends \markhuot\craftpest\overrides\ProjectConfig
 {
-    public function saveModifiedConfigData(bool $writeExternalConfig = null): void
+    public function saveModifiedConfigData(?bool $writeExternalConfig = null): void
     {
         // no-op since we don't ever want to save config data back to the DB in a test
     }
diff --git a/src/http/RequestBuilder.php b/src/http/RequestBuilder.php
index b4d9bba..9296c4e 100644
--- a/src/http/RequestBuilder.php
+++ b/src/http/RequestBuilder.php
@@ -26,8 +26,8 @@ class RequestBuilder
     public function __construct(
         string $method,
         string $uri,
-        \craft\web\Application $app = null,
-        RequestHandler $handler = null,
+        ?\craft\web\Application $app = null,
+        ?RequestHandler $handler = null,
     ) {
         $this->method = $method;
         $this->app = $app ?? \Craft::$app;
diff --git a/src/http/RequestHandler.php b/src/http/RequestHandler.php
index dcd55e2..439b08f 100644
--- a/src/http/RequestHandler.php
+++ b/src/http/RequestHandler.php
@@ -14,7 +14,7 @@ class RequestHandler
 {
     private \craft\web\Application $app;
 
-    public function __construct(\craft\web\Application $app = null)
+    public function __construct(?\craft\web\Application $app = null)
     {
         $this->app = $app ?? \Craft::$app;
     }
diff --git a/src/illuminate/AssertableJsonString.php b/src/illuminate/AssertableJsonString.php
index 309d317..b802494 100644
--- a/src/illuminate/AssertableJsonString.php
+++ b/src/illuminate/AssertableJsonString.php
@@ -246,7 +246,7 @@ public function assertPath($path, $expect)
      * @param  array|null  $responseData
      * @return $this
      */
-    public function assertStructure(array $structure = null, $responseData = null)
+    public function assertStructure(?array $structure = null, $responseData = null)
     {
         if (is_null($structure)) {
             return $this->assertSimilar($this->decoded);
diff --git a/src/test/ActingAs.php b/src/test/ActingAs.php
index f8a3695..2f8cdd4 100644
--- a/src/test/ActingAs.php
+++ b/src/test/ActingAs.php
@@ -23,7 +23,7 @@ trait ActingAs
      * 4. A callable that returns a User element, `->actingAs(fn () => $someUser)`
      * 5. `null` to log the user out for the given request
      */
-    public function actingAs(UserFactory|User|string|callable $userOrName = null): self
+    public function actingAs(UserFactory|User|string|callable|null $userOrName = null): self
     {
         if (is_null($userOrName)) {
             \Craft::$app->getUser()->logout(false);