diff --git a/src/Control/Director.php b/src/Control/Director.php
index 119d4e746d0..966dea3c33b 100644
--- a/src/Control/Director.php
+++ b/src/Control/Director.php
@@ -486,7 +486,7 @@ protected static function validateUserAndPass($url)
      * @param HTTPRequest $request
      * @return string Host name, including port (if present)
      */
-    public static function host(HTTPRequest $request = null)
+    public static function host(?HTTPRequest $request = null)
     {
         // Check if overridden by alternate_base_url
         if ($baseURL = static::config()->get('alternate_base_url')) {
@@ -528,7 +528,7 @@ public static function host(HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return int|null
      */
-    public static function port(HTTPRequest $request = null)
+    public static function port(?HTTPRequest $request = null)
     {
         $host = static::host($request);
         return (int)parse_url($host ?? '', PHP_URL_PORT) ?: null;
@@ -540,7 +540,7 @@ public static function port(HTTPRequest $request = null)
      * @param HTTPRequest|null $request
      * @return string|null
      */
-    public static function hostName(HTTPRequest $request = null)
+    public static function hostName(?HTTPRequest $request = null)
     {
         $host = static::host($request);
         return parse_url($host ?? '', PHP_URL_HOST) ?: null;
@@ -553,7 +553,7 @@ public static function hostName(HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return bool|string
      */
-    public static function protocolAndHost(HTTPRequest $request = null)
+    public static function protocolAndHost(?HTTPRequest $request = null)
     {
         return static::protocol($request) . static::host($request);
     }
@@ -564,7 +564,7 @@ public static function protocolAndHost(HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return string
      */
-    public static function protocol(HTTPRequest $request = null)
+    public static function protocol(?HTTPRequest $request = null)
     {
         return (Director::is_https($request)) ? 'https://' : 'http://';
     }
@@ -575,7 +575,7 @@ public static function protocol(HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return bool
      */
-    public static function is_https(HTTPRequest $request = null)
+    public static function is_https(?HTTPRequest $request = null)
     {
         // Check override from alternate_base_url
         if ($baseURL = static::config()->uninherited('alternate_base_url')) {
@@ -900,7 +900,7 @@ public static function absoluteBaseURL()
      * @param HTTPRequest|null $request
      * @return string
      */
-    public static function absoluteBaseURLWithAuth(HTTPRequest $request = null)
+    public static function absoluteBaseURLWithAuth(?HTTPRequest $request = null)
     {
         // Detect basic auth
         $login = '';
@@ -960,7 +960,7 @@ protected static function force_redirect($destURL)
      * Can include port number.
      * @param HTTPRequest|null $request Request object to check
      */
-    public static function forceSSL($patterns = null, $secureDomain = null, HTTPRequest $request = null)
+    public static function forceSSL($patterns = null, $secureDomain = null, ?HTTPRequest $request = null)
     {
         $handler = CanonicalURLMiddleware::singleton()->setForceSSL(true);
         if ($patterns) {
@@ -977,7 +977,7 @@ public static function forceSSL($patterns = null, $secureDomain = null, HTTPRequ
      *
      * @param HTTPRequest $request
      */
-    public static function forceWWW(HTTPRequest $request = null)
+    public static function forceWWW(?HTTPRequest $request = null)
     {
         $handler = CanonicalURLMiddleware::singleton()->setForceWWW(true);
         $handler->throwRedirectIfNeeded($request);
@@ -993,7 +993,7 @@ public static function forceWWW(HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return bool
      */
-    public static function is_ajax(HTTPRequest $request = null)
+    public static function is_ajax(?HTTPRequest $request = null)
     {
         $request = Director::currentRequest($request);
         if ($request) {
@@ -1038,7 +1038,7 @@ public static function get_environment_type()
      *
      * @return string|null null if not overridden, otherwise the actual value
      */
-    public static function get_session_environment_type(HTTPRequest $request = null)
+    public static function get_session_environment_type(?HTTPRequest $request = null)
     {
         $request = static::currentRequest($request);
 
@@ -1114,7 +1114,7 @@ public static function get_template_global_variables()
      * @param HTTPRequest $request
      * @return HTTPRequest Request object if one is both current and valid
      */
-    protected static function currentRequest(HTTPRequest $request = null)
+    protected static function currentRequest(?HTTPRequest $request = null)
     {
         // Ensure we only use a registered HTTPRequest and don't
         // incidentally construct a singleton
diff --git a/src/Control/Email/Email.php b/src/Control/Email/Email.php
index 52b05dc944f..0f3e967a729 100644
--- a/src/Control/Email/Email.php
+++ b/src/Control/Email/Email.php
@@ -226,7 +226,7 @@ private function getDefaultFrom(): string|array
     /**
      * Passing a string of HTML for $body will have no affect if you also call either setData() or addData()
      */
-    public function setBody(AbstractPart|string $body = null): static
+    public function setBody(AbstractPart|string|null $body = null): static
     {
         if ($body instanceof AbstractPart) {
             // pass to Symfony\Component\Mime\Message::setBody()
@@ -324,7 +324,7 @@ public function addAttachment(string $path, ?string $alias = null, ?string $mime
         return $this->attachFromPath($path, $alias, $mime);
     }
 
-    public function addAttachmentFromData(string $data, string $name, string $mime = null): static
+    public function addAttachmentFromData(string $data, string $name, ?string $mime = null): static
     {
         return $this->attach($data, $name, $mime);
     }
diff --git a/src/Control/Middleware/CanonicalURLMiddleware.php b/src/Control/Middleware/CanonicalURLMiddleware.php
index 66e2a2afe60..449da1b0007 100644
--- a/src/Control/Middleware/CanonicalURLMiddleware.php
+++ b/src/Control/Middleware/CanonicalURLMiddleware.php
@@ -308,7 +308,7 @@ protected function getRedirect(HTTPRequest $request)
      * @param HTTPRequest|null $request Allow HTTPRequest to be used for the base comparison
      * @throws HTTPResponse_Exception
      */
-    public function throwRedirectIfNeeded(HTTPRequest $request = null)
+    public function throwRedirectIfNeeded(?HTTPRequest $request = null)
     {
         $request = $this->getOrValidateRequest($request);
         if (!$request) {
@@ -326,7 +326,7 @@ public function throwRedirectIfNeeded(HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return HTTPRequest|null
      */
-    protected function getOrValidateRequest(HTTPRequest $request = null)
+    protected function getOrValidateRequest(?HTTPRequest $request = null)
     {
         if ($request instanceof HTTPRequest) {
             return $request;
@@ -524,7 +524,7 @@ protected function isEnabled()
      * @param HTTPResponse $response
      * @return bool
      */
-    protected function hasBasicAuthPrompt(HTTPResponse $response = null)
+    protected function hasBasicAuthPrompt(?HTTPResponse $response = null)
     {
         if (!$response) {
             return false;
diff --git a/src/Control/Middleware/RequestHandlerMiddlewareAdapter.php b/src/Control/Middleware/RequestHandlerMiddlewareAdapter.php
index 561199fb619..cbfee9d2f9a 100644
--- a/src/Control/Middleware/RequestHandlerMiddlewareAdapter.php
+++ b/src/Control/Middleware/RequestHandlerMiddlewareAdapter.php
@@ -18,7 +18,7 @@ class RequestHandlerMiddlewareAdapter extends RequestHandler
      */
     protected $requestHandler = null;
 
-    public function __construct(RequestHandler $handler = null)
+    public function __construct(?RequestHandler $handler = null)
     {
         if ($handler) {
             $this->setRequestHandler($handler);
diff --git a/src/Control/PjaxResponseNegotiator.php b/src/Control/PjaxResponseNegotiator.php
index 70d3b76570b..71d765ecd64 100644
--- a/src/Control/PjaxResponseNegotiator.php
+++ b/src/Control/PjaxResponseNegotiator.php
@@ -41,7 +41,7 @@ class PjaxResponseNegotiator
      * @param array $callbacks
      * @param HTTPResponse $response An existing response to reuse (optional)
      */
-    public function __construct($callbacks = [], HTTPResponse $response = null)
+    public function __construct($callbacks = [], ?HTTPResponse $response = null)
     {
         $this->callbacks = $callbacks;
         $this->response = $response ?: HTTPResponse::create();
diff --git a/src/Control/Session.php b/src/Control/Session.php
index 51194b3783a..59ac008c099 100644
--- a/src/Control/Session.php
+++ b/src/Control/Session.php
@@ -404,7 +404,7 @@ private function isCookieSecure(string $sameSite, bool $isHttps): bool
      * @param bool $removeCookie
      * @param HTTPRequest $request The request for which to destroy a session
      */
-    public function destroy($removeCookie = true, HTTPRequest $request = null)
+    public function destroy($removeCookie = true, ?HTTPRequest $request = null)
     {
         if (session_id()) {
             if ($removeCookie) {
diff --git a/src/Core/BaseKernel.php b/src/Core/BaseKernel.php
index a1dbc503ba5..16885a50182 100644
--- a/src/Core/BaseKernel.php
+++ b/src/Core/BaseKernel.php
@@ -2,6 +2,7 @@
 
 namespace SilverStripe\Core;
 
+use Exception;
 use InvalidArgumentException;
 use Monolog\Handler\StreamHandler;
 use Monolog\Logger;
@@ -21,13 +22,12 @@
 use SilverStripe\Core\Manifest\ModuleLoader;
 use SilverStripe\Core\Manifest\ModuleManifest;
 use SilverStripe\Dev\DebugView;
+use SilverStripe\Dev\Deprecation;
 use SilverStripe\Logging\ErrorHandler;
 use SilverStripe\View\PublicThemes;
 use SilverStripe\View\SSViewer;
 use SilverStripe\View\ThemeManifest;
 use SilverStripe\View\ThemeResourceLoader;
-use Exception;
-use SilverStripe\Dev\Deprecation;
 
 /**
  * Simple Kernel container
@@ -142,10 +142,10 @@ protected function bootPHP()
     {
         if ($this->getEnvironment() === BaseKernel::LIVE) {
             // limited to fatal errors and warnings in live mode
-            error_reporting(E_ALL & ~(E_DEPRECATED | E_STRICT | E_NOTICE));
+            error_reporting(E_ALL & ~(E_DEPRECATED | E_NOTICE));
         } else {
             // Report all errors in dev / test mode
-            error_reporting(E_ALL | E_STRICT);
+            error_reporting(E_ALL);
         }
 
         /**
diff --git a/src/Core/Cache/DefaultCacheFactory.php b/src/Core/Cache/DefaultCacheFactory.php
index b82d6f08a2b..77acafe61bb 100644
--- a/src/Core/Cache/DefaultCacheFactory.php
+++ b/src/Core/Cache/DefaultCacheFactory.php
@@ -39,7 +39,7 @@ class DefaultCacheFactory implements CacheFactory
      * @param array $args List of global options to merge with args during create()
      * @param LoggerInterface $logger Logger instance to assign
      */
-    public function __construct($args = [], LoggerInterface $logger = null)
+    public function __construct($args = [], ?LoggerInterface $logger = null)
     {
         $this->args = $args;
         $this->logger = $logger;
diff --git a/src/Core/Cache/ManifestCacheFactory.php b/src/Core/Cache/ManifestCacheFactory.php
index 52d3b294fe2..9481a1c8251 100644
--- a/src/Core/Cache/ManifestCacheFactory.php
+++ b/src/Core/Cache/ManifestCacheFactory.php
@@ -17,7 +17,7 @@
  */
 class ManifestCacheFactory extends DefaultCacheFactory
 {
-    public function __construct(array $args = [], LoggerInterface $logger = null)
+    public function __construct(array $args = [], ?LoggerInterface $logger = null)
     {
         // Build default manifest logger
         if (!$logger) {
diff --git a/src/Core/Cache/MemcachedCacheFactory.php b/src/Core/Cache/MemcachedCacheFactory.php
index 1752baf5ba9..a511ce6f208 100644
--- a/src/Core/Cache/MemcachedCacheFactory.php
+++ b/src/Core/Cache/MemcachedCacheFactory.php
@@ -18,7 +18,7 @@ class MemcachedCacheFactory implements CacheFactory
     /**
      * @param Memcached $memcachedClient
      */
-    public function __construct(Memcached $memcachedClient = null)
+    public function __construct(?Memcached $memcachedClient = null)
     {
         $this->memcachedClient = $memcachedClient;
     }
diff --git a/src/Core/Config/CoreConfigFactory.php b/src/Core/Config/CoreConfigFactory.php
index c607a10e636..3d76c300b1a 100644
--- a/src/Core/Config/CoreConfigFactory.php
+++ b/src/Core/Config/CoreConfigFactory.php
@@ -33,7 +33,7 @@ class CoreConfigFactory
      *
      * @param CacheFactory $cacheFactory
      */
-    public function __construct(CacheFactory $cacheFactory = null)
+    public function __construct(?CacheFactory $cacheFactory = null)
     {
         $this->cacheFactory = $cacheFactory;
     }
diff --git a/src/Core/Manifest/ClassManifest.php b/src/Core/Manifest/ClassManifest.php
index 0e2887635ab..b1385729067 100644
--- a/src/Core/Manifest/ClassManifest.php
+++ b/src/Core/Manifest/ClassManifest.php
@@ -198,7 +198,7 @@ class ClassManifest
      * @param string $base The manifest base path.
      * @param CacheFactory $cacheFactory Optional cache to use. Set to null to not cache.
      */
-    public function __construct($base, CacheFactory $cacheFactory = null)
+    public function __construct($base, ?CacheFactory $cacheFactory = null)
     {
         $this->base = $base;
         $this->cacheFactory = $cacheFactory;
diff --git a/src/Core/Manifest/ModuleManifest.php b/src/Core/Manifest/ModuleManifest.php
index bb8f29a50bd..6e0681f425f 100644
--- a/src/Core/Manifest/ModuleManifest.php
+++ b/src/Core/Manifest/ModuleManifest.php
@@ -73,7 +73,7 @@ class ModuleManifest
      * @param string $base The project base path.
      * @param CacheFactory $cacheFactory Cache factory to use
      */
-    public function __construct($base, CacheFactory $cacheFactory = null)
+    public function __construct($base, ?CacheFactory $cacheFactory = null)
     {
         $this->base = $base;
         $this->cacheKey = sha1($base ?? '') . '_modules';
diff --git a/src/Dev/Debug.php b/src/Dev/Debug.php
index 5701577f08f..d1db47671dc 100644
--- a/src/Dev/Debug.php
+++ b/src/Dev/Debug.php
@@ -38,7 +38,7 @@ class Debug
      * @param bool $showHeader
      * @param HTTPRequest|null $request
      */
-    public static function show($val, $showHeader = true, HTTPRequest $request = null)
+    public static function show($val, $showHeader = true, ?HTTPRequest $request = null)
     {
         // Don't show on live
         if (Director::isLive()) {
@@ -80,7 +80,7 @@ public static function caller()
      * @param bool $showHeader
      * @param HTTPRequest $request
      */
-    public static function endshow($val, $showHeader = true, HTTPRequest $request = null)
+    public static function endshow($val, $showHeader = true, ?HTTPRequest $request = null)
     {
         // Don't show on live
         if (Director::isLive()) {
@@ -100,7 +100,7 @@ public static function endshow($val, $showHeader = true, HTTPRequest $request =
      * @param mixed $val
      * @param HTTPRequest $request Current request to influence output format
      */
-    public static function dump($val, HTTPRequest $request = null)
+    public static function dump($val, ?HTTPRequest $request = null)
     {
         echo Debug::create_debug_view($request)
             ->renderVariable($val, Debug::caller());
@@ -113,7 +113,7 @@ public static function dump($val, HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return string
      */
-    public static function text($val, HTTPRequest $request = null)
+    public static function text($val, ?HTTPRequest $request = null)
     {
         return static::create_debug_view($request)
             ->debugVariableText($val);
@@ -127,7 +127,7 @@ public static function text($val, HTTPRequest $request = null)
      * @param bool $showHeader
      * @param HTTPRequest|null $request
      */
-    public static function message($message, $showHeader = true, HTTPRequest $request = null)
+    public static function message($message, $showHeader = true, ?HTTPRequest $request = null)
     {
         // Don't show on live
         if (Director::isLive()) {
@@ -144,7 +144,7 @@ public static function message($message, $showHeader = true, HTTPRequest $reques
      * @param HTTPRequest $request Optional request to target this view for
      * @return DebugView
      */
-    public static function create_debug_view(HTTPRequest $request = null)
+    public static function create_debug_view(?HTTPRequest $request = null)
     {
         $service = static::supportsHTML($request)
             ? DebugView::class
@@ -158,7 +158,7 @@ public static function create_debug_view(HTTPRequest $request = null)
      * @param HTTPRequest $request
      * @return bool
      */
-    protected static function supportsHTML(HTTPRequest $request = null)
+    protected static function supportsHTML(?HTTPRequest $request = null)
     {
         // No HTML output in CLI
         if (Director::is_cli()) {
diff --git a/src/Dev/DebugView.php b/src/Dev/DebugView.php
index c1953031abb..65f5f91cd64 100644
--- a/src/Dev/DebugView.php
+++ b/src/Dev/DebugView.php
@@ -102,10 +102,6 @@ class DebugView
             'title' => 'User Warning',
             'class' => 'warning'
         ],
-        E_STRICT => [
-            'title' => 'Strict Notice',
-            'class' => 'notice'
-        ],
         E_RECOVERABLE_ERROR => [
             'title' => 'Recoverable Error',
             'class' => 'warning'
diff --git a/src/Dev/FunctionalTest.php b/src/Dev/FunctionalTest.php
index 3adadde3dc4..1b37946dbf3 100644
--- a/src/Dev/FunctionalTest.php
+++ b/src/Dev/FunctionalTest.php
@@ -193,7 +193,7 @@ public function post($url, $data, $headers = null, $session = null, $body = null
      * @param array $data Map of GET/POST data.
      * @param bool $withSecurityToken Submit with the form's security token if there is one.
      */
-    public function submitForm(string $formID, string $button = null, array $data = [], bool $withSecurityToken = true): HTTPResponse
+    public function submitForm(string $formID, ?string $button = null, array $data = [], bool $withSecurityToken = true): HTTPResponse
     {
         $this->cssParser = null;
         $response = $this->mainSession->submitForm($formID, $button, $data, $withSecurityToken);
diff --git a/src/Dev/TestMailer.php b/src/Dev/TestMailer.php
index 7bfe228acc1..4fc7ad1b627 100644
--- a/src/Dev/TestMailer.php
+++ b/src/Dev/TestMailer.php
@@ -33,7 +33,7 @@ public function __construct(
         $this->dispatcher = $dispatcher;
     }
 
-    public function send(RawMessage $message, Envelope $envelope = null): void
+    public function send(RawMessage $message, ?Envelope $envelope = null): void
     {
         if (!is_a($message, Email::class)) {
             throw new InvalidArgumentException('$message must be a ' . Email::class);
@@ -122,7 +122,7 @@ private function convertAddressesToString(array $addresses): string
         return implode(',', array_map(fn(Address $address) => $address->getAddress(), $addresses));
     }
 
-    private function dispatchEvent(Email $email, Envelope $envelope = null): void
+    private function dispatchEvent(Email $email, ?Envelope $envelope = null): void
     {
         $sender = $email->getSender()[0] ?? $email->getFrom()[0] ?? new Address('test.sender@example.com');
         $recipients = empty($email->getTo()) ? [new Address('test.recipient@example.com')] : $email->getTo();
diff --git a/src/Dev/TestSession.php b/src/Dev/TestSession.php
index 2c1ff07a659..d67c124d4ec 100644
--- a/src/Dev/TestSession.php
+++ b/src/Dev/TestSession.php
@@ -206,7 +206,7 @@ public function sendRequest($method, $url, $data, $headers = null, $session = nu
      * @param array $data Map of GET/POST data.
      * @param bool $withSecurityToken Submit with the form's security token if there is one.
      */
-    public function submitForm(string $formID, string $button = null, array $data = [], bool $withSecurityToken = true): HTTPResponse
+    public function submitForm(string $formID, ?string $button = null, array $data = [], bool $withSecurityToken = true): HTTPResponse
     {
         $page = $this->lastPage();
         if ($page) {
diff --git a/src/Forms/DefaultFormFactory.php b/src/Forms/DefaultFormFactory.php
index 8b737d0481e..733f8cc085f 100644
--- a/src/Forms/DefaultFormFactory.php
+++ b/src/Forms/DefaultFormFactory.php
@@ -33,7 +33,7 @@ public function __construct()
      * @return Form
      * @throws InvalidArgumentException When required context is missing
      */
-    public function getForm(RequestHandler $controller = null, $name = FormFactory::DEFAULT_NAME, $context = [])
+    public function getForm(?RequestHandler $controller = null, $name = FormFactory::DEFAULT_NAME, $context = [])
     {
         // Validate context
         foreach ($this->getRequiredContext() as $required) {
@@ -64,7 +64,7 @@ public function getForm(RequestHandler $controller = null, $name = FormFactory::
      * @param array $context
      * @return FieldList
      */
-    protected function getFormFields(RequestHandler $controller = null, $name, $context = [])
+    protected function getFormFields(?RequestHandler $controller = null, $name, $context = [])
     {
         // Fall back to standard "getCMSFields" which itself uses the FormScaffolder as a fallback
         $fields = $context['Record']->getCMSFields();
@@ -80,7 +80,7 @@ protected function getFormFields(RequestHandler $controller = null, $name, $cont
      * @param array $context
      * @return FieldList
      */
-    protected function getFormActions(RequestHandler $controller = null, $name, $context = [])
+    protected function getFormActions(?RequestHandler $controller = null, $name, $context = [])
     {
         $actions = $context['Record']->getCMSActions();
         $this->invokeWithExtensions('updateFormActions', $actions, $controller, $name, $context);
@@ -93,7 +93,7 @@ protected function getFormActions(RequestHandler $controller = null, $name, $con
      * @param array $context
      * @return null|Validator
      */
-    protected function getFormValidator(RequestHandler $controller = null, $name, $context = [])
+    protected function getFormValidator(?RequestHandler $controller = null, $name, $context = [])
     {
         if (!$context['Record'] instanceof DataObject) {
             return null;
diff --git a/src/Forms/Form.php b/src/Forms/Form.php
index 69151c12145..91a23da0400 100644
--- a/src/Forms/Form.php
+++ b/src/Forms/Form.php
@@ -277,11 +277,11 @@ class Form extends ViewableData implements HasRequestHandler
      * @param Validator|null $validator Override the default validator instance (Default: {@link RequiredFields})
      */
     public function __construct(
-        RequestHandler $controller = null,
+        ?RequestHandler $controller = null,
         $name = Form::DEFAULT_NAME,
-        FieldList $fields = null,
-        FieldList $actions = null,
-        Validator $validator = null
+        ?FieldList $fields = null,
+        ?FieldList $actions = null,
+        ?Validator $validator = null
     ) {
         parent::__construct();
 
@@ -1130,7 +1130,7 @@ public function getController()
      * @param RequestHandler $controller
      * @return $this
      */
-    public function setController(RequestHandler $controller = null)
+    public function setController(?RequestHandler $controller = null)
     {
         $this->controller = $controller;
         return $this;
diff --git a/src/Forms/FormFactory.php b/src/Forms/FormFactory.php
index b900fbcd2fd..d953608bb13 100644
--- a/src/Forms/FormFactory.php
+++ b/src/Forms/FormFactory.php
@@ -25,7 +25,7 @@ interface FormFactory
      * Custom factories may support more advanced parameters.
      * @return Form
      */
-    public function getForm(RequestHandler $controller = null, $name = FormFactory::DEFAULT_NAME, $context = []);
+    public function getForm(?RequestHandler $controller = null, $name = FormFactory::DEFAULT_NAME, $context = []);
 
     /**
      * Return list of mandatory context keys
diff --git a/src/Forms/GridField/GridField.php b/src/Forms/GridField/GridField.php
index d6039fe4c93..dfd857ce5d2 100644
--- a/src/Forms/GridField/GridField.php
+++ b/src/Forms/GridField/GridField.php
@@ -157,7 +157,7 @@ class GridField extends FormField
      * @param SS_List $dataList
      * @param GridFieldConfig $config
      */
-    public function __construct($name, $title = null, SS_List $dataList = null, GridFieldConfig $config = null)
+    public function __construct($name, $title = null, ?SS_List $dataList = null, ?GridFieldConfig $config = null)
     {
         parent::__construct($name, $title, null);
 
diff --git a/src/Forms/HTMLEditor/HTMLEditorConfig.php b/src/Forms/HTMLEditor/HTMLEditorConfig.php
index 6c685bf29c5..b35d7d4b165 100644
--- a/src/Forms/HTMLEditor/HTMLEditorConfig.php
+++ b/src/Forms/HTMLEditor/HTMLEditorConfig.php
@@ -95,7 +95,7 @@ public static function get($identifier = null)
      * @param HTMLEditorConfig $config Config to set, or null to clear
      * @return HTMLEditorConfig The assigned config
      */
-    public static function set_config($identifier, HTMLEditorConfig $config = null)
+    public static function set_config($identifier, ?HTMLEditorConfig $config = null)
     {
         if ($config) {
             HTMLEditorConfig::$configs[$identifier] = $config;
diff --git a/src/Forms/Schema/FormSchema.php b/src/Forms/Schema/FormSchema.php
index a8b712a14e7..04fa74b0f98 100644
--- a/src/Forms/Schema/FormSchema.php
+++ b/src/Forms/Schema/FormSchema.php
@@ -50,7 +50,7 @@ class FormSchema
      * @param ValidationResult $result Required for 'error' response
      * @return array
      */
-    public function getMultipartSchema($schemaParts, $schemaID, Form $form = null, ValidationResult $result = null)
+    public function getMultipartSchema($schemaParts, $schemaID, ?Form $form = null, ?ValidationResult $result = null)
     {
         if (!is_array($schemaParts)) {
             $schemaParts = preg_split('#\s*,\s*#', $schemaParts ?? '') ?: [];
diff --git a/src/ORM/DataExtension.php b/src/ORM/DataExtension.php
index 1644ee1b7ef..ecf5c0f717a 100644
--- a/src/ORM/DataExtension.php
+++ b/src/ORM/DataExtension.php
@@ -48,7 +48,7 @@ public function validate(ValidationResult $validationResult)
      * @param SQLSelect $query Query to augment.
      * @param DataQuery $dataQuery Container DataQuery for this SQLSelect
      */
-    public function augmentSQL(SQLSelect $query, DataQuery $dataQuery = null)
+    public function augmentSQL(SQLSelect $query, ?DataQuery $dataQuery = null)
     {
     }
 
diff --git a/src/Security/Authenticator.php b/src/Security/Authenticator.php
index 856f65654e2..87ffc1924d0 100644
--- a/src/Security/Authenticator.php
+++ b/src/Security/Authenticator.php
@@ -110,7 +110,7 @@ public function getLostPasswordHandler($link);
      * @param ValidationResult $result A validationresult which is either valid or contains the error message(s)
      * @return Member The matched member, or null if the authentication fails
      */
-    public function authenticate(array $data, HTTPRequest $request, ValidationResult &$result = null);
+    public function authenticate(array $data, HTTPRequest $request, ?ValidationResult &$result = null);
 
     /**
      * Check if the passed password matches the stored one (if the member is not locked out).
@@ -123,5 +123,5 @@ public function authenticate(array $data, HTTPRequest $request, ValidationResult
      * @param ValidationResult $result
      * @return ValidationResult
      */
-    public function checkPassword(Member $member, $password, ValidationResult &$result = null);
+    public function checkPassword(Member $member, $password, ?ValidationResult &$result = null);
 }
diff --git a/src/Security/BasicAuth.php b/src/Security/BasicAuth.php
index d99d7802d90..ad13d131652 100644
--- a/src/Security/BasicAuth.php
+++ b/src/Security/BasicAuth.php
@@ -207,7 +207,7 @@ public static function protect_entire_site($protect = true, $code = BasicAuth::A
      * @param HTTPRequest|null $request
      * @throws HTTPResponse_Exception
      */
-    public static function protect_site_if_necessary(HTTPRequest $request = null)
+    public static function protect_site_if_necessary(?HTTPRequest $request = null)
     {
         $config = static::config();
 
diff --git a/src/Security/DefaultPermissionChecker.php b/src/Security/DefaultPermissionChecker.php
index 0982846432b..6d3ed3a4d46 100644
--- a/src/Security/DefaultPermissionChecker.php
+++ b/src/Security/DefaultPermissionChecker.php
@@ -16,7 +16,7 @@ interface DefaultPermissionChecker
      * @param Member $member
      * @return bool
      */
-    public function canEdit(Member $member = null);
+    public function canEdit(?Member $member = null);
 
     /**
      * Can root be viewed?
@@ -24,7 +24,7 @@ public function canEdit(Member $member = null);
      * @param Member $member
      * @return bool
      */
-    public function canView(Member $member = null);
+    public function canView(?Member $member = null);
 
     /**
      * Can root be deleted?
@@ -32,7 +32,7 @@ public function canView(Member $member = null);
      * @param Member $member
      * @return bool
      */
-    public function canDelete(Member $member = null);
+    public function canDelete(?Member $member = null);
 
     /**
      * Can root objects be created?
@@ -40,5 +40,5 @@ public function canDelete(Member $member = null);
      * @param Member $member
      * @return bool
      */
-    public function canCreate(Member $member = null);
+    public function canCreate(?Member $member = null);
 }
diff --git a/src/Security/IdentityStore.php b/src/Security/IdentityStore.php
index 6a07f1653bc..4f25955575d 100644
--- a/src/Security/IdentityStore.php
+++ b/src/Security/IdentityStore.php
@@ -19,12 +19,12 @@ interface IdentityStore
      * @param Boolean $persistent boolean If set to true, the login may persist beyond the current session.
      * @param HTTPRequest $request The request of the visitor that is logging in, to get, for example, cookies.
      */
-    public function logIn(Member $member, $persistent = false, HTTPRequest $request = null);
+    public function logIn(Member $member, $persistent = false, ?HTTPRequest $request = null);
 
     /**
      * Log any logged-in member out of this identity store.
      *
      * @param HTTPRequest $request The request of the visitor that is logging out, to get, for example, cookies.
      */
-    public function logOut(HTTPRequest $request = null);
+    public function logOut(?HTTPRequest $request = null);
 }
diff --git a/src/Security/InheritedPermissions.php b/src/Security/InheritedPermissions.php
index 65b66044819..9b06cce28dd 100644
--- a/src/Security/InheritedPermissions.php
+++ b/src/Security/InheritedPermissions.php
@@ -103,7 +103,7 @@ class InheritedPermissions implements PermissionChecker, MemberCacheFlusher
      * @param string $baseClass Base class
      * @param CacheInterface $cache
      */
-    public function __construct($baseClass, CacheInterface $cache = null)
+    public function __construct($baseClass, ?CacheInterface $cache = null)
     {
         if (!is_a($baseClass, DataObject::class, true)) {
             throw new InvalidArgumentException('Invalid DataObject class: ' . $baseClass);
@@ -249,7 +249,7 @@ public function prePopulatePermissionCache($permission = 'edit', $ids = [])
     protected function batchPermissionCheck(
         $type,
         $ids,
-        Member $member = null,
+        ?Member $member = null,
         $globalPermission = [],
         $useCached = true
     ) {
@@ -353,7 +353,7 @@ protected function batchPermissionCheckForStage(
         $globalPermission,
         DataList $stageRecords,
         $groupIDsSQLList,
-        Member $member = null
+        ?Member $member = null
     ) {
         // Initialise all IDs to false
         $result = array_fill_keys($stageRecords->column('ID') ?? [], false);
@@ -453,7 +453,7 @@ protected function batchPermissionCheckForStage(
      * @param bool $useCached
      * @return array
      */
-    public function canEditMultiple($ids, Member $member = null, $useCached = true)
+    public function canEditMultiple($ids, ?Member $member = null, $useCached = true)
     {
         return $this->batchPermissionCheck(
             InheritedPermissions::EDIT,
@@ -470,7 +470,7 @@ public function canEditMultiple($ids, Member $member = null, $useCached = true)
      * @param bool $useCached
      * @return array
      */
-    public function canViewMultiple($ids, Member $member = null, $useCached = true)
+    public function canViewMultiple($ids, ?Member $member = null, $useCached = true)
     {
         return $this->batchPermissionCheck(InheritedPermissions::VIEW, $ids, $member, [], $useCached);
     }
@@ -481,7 +481,7 @@ public function canViewMultiple($ids, Member $member = null, $useCached = true)
      * @param bool $useCached
      * @return array
      */
-    public function canDeleteMultiple($ids, Member $member = null, $useCached = true)
+    public function canDeleteMultiple($ids, ?Member $member = null, $useCached = true)
     {
         // Validate ids
         $ids = array_filter($ids ?? [], 'is_numeric');
@@ -555,7 +555,7 @@ public function canDeleteMultiple($ids, Member $member = null, $useCached = true
      * @param Member|null $member
      * @return bool|mixed
      */
-    public function canDelete($id, Member $member = null)
+    public function canDelete($id, ?Member $member = null)
     {
         // No ID: Check default permission
         if (!$id) {
@@ -577,7 +577,7 @@ public function canDelete($id, Member $member = null)
      * @param Member|null $member
      * @return bool|mixed
      */
-    public function canEdit($id, Member $member = null)
+    public function canEdit($id, ?Member $member = null)
     {
         // No ID: Check default permission
         if (!$id) {
@@ -599,7 +599,7 @@ public function canEdit($id, Member $member = null)
      * @param Member|null $member
      * @return bool|mixed
      */
-    public function canView($id, Member $member = null)
+    public function canView($id, ?Member $member = null)
     {
         // No ID: Check default permission
         if (!$id) {
@@ -700,7 +700,7 @@ protected function getMemberJoinTable($type)
      * @param Member $member
      * @return bool
      */
-    protected function checkDefaultPermissions($type, Member $member = null)
+    protected function checkDefaultPermissions($type, ?Member $member = null)
     {
         $defaultPermissions = $this->getDefaultPermissions();
         if (!$defaultPermissions) {
diff --git a/src/Security/LogoutForm.php b/src/Security/LogoutForm.php
index 03ad3a05965..5b12c2c3563 100644
--- a/src/Security/LogoutForm.php
+++ b/src/Security/LogoutForm.php
@@ -22,11 +22,11 @@ class LogoutForm extends Form
      * {@inheritdoc}
      */
     public function __construct(
-        RequestHandler $controller = null,
+        ?RequestHandler $controller = null,
         $name = LogoutForm::DEFAULT_NAME,
-        FieldList $fields = null,
-        FieldList $actions = null,
-        Validator $validator = null
+        ?FieldList $fields = null,
+        ?FieldList $actions = null,
+        ?Validator $validator = null
     ) {
         $this->setController($controller);
 
diff --git a/src/Security/Member.php b/src/Security/Member.php
index a3c3dc0d7f4..e419423e13b 100644
--- a/src/Security/Member.php
+++ b/src/Security/Member.php
@@ -310,7 +310,7 @@ public function canLogin()
      * @param ValidationResult $result Optional result to add errors to
      * @return ValidationResult
      */
-    public function validateCanLogin(ValidationResult &$result = null)
+    public function validateCanLogin(?ValidationResult &$result = null)
     {
         $result = $result ?: ValidationResult::create();
         if ($this->isLockedOut()) {
@@ -379,7 +379,7 @@ public function isLockedOut()
      *
      * @param PasswordValidator $validator
      */
-    public static function set_password_validator(PasswordValidator $validator = null)
+    public static function set_password_validator(?PasswordValidator $validator = null)
     {
         // Override existing config
         Config::modify()->remove(Injector::class, PasswordValidator::class);
@@ -493,7 +493,7 @@ public function regenerateTempID()
      *
      * @param HTTPRequest|null $request
      */
-    public function beforeMemberLoggedOut(HTTPRequest $request = null)
+    public function beforeMemberLoggedOut(?HTTPRequest $request = null)
     {
         $this->extend('beforeMemberLoggedOut', $request);
     }
@@ -503,7 +503,7 @@ public function beforeMemberLoggedOut(HTTPRequest $request = null)
      *
      * @param HTTPRequest|null $request
      */
-    public function afterMemberLoggedOut(HTTPRequest $request = null)
+    public function afterMemberLoggedOut(?HTTPRequest $request = null)
     {
         $this->extend('afterMemberLoggedOut', $request);
     }
diff --git a/src/Security/MemberAuthenticator/CMSMemberAuthenticator.php b/src/Security/MemberAuthenticator/CMSMemberAuthenticator.php
index 467823b4d1b..a60a3d31c32 100644
--- a/src/Security/MemberAuthenticator/CMSMemberAuthenticator.php
+++ b/src/Security/MemberAuthenticator/CMSMemberAuthenticator.php
@@ -23,7 +23,7 @@ public function supportedServices()
      * @param Member|null $member
      * @return Member
      */
-    protected function authenticateMember($data, ValidationResult &$result = null, Member $member = null)
+    protected function authenticateMember($data, ?ValidationResult &$result = null, ?Member $member = null)
     {
         // Attempt to identify by temporary ID
         if (!empty($data['tempid'])) {
diff --git a/src/Security/MemberAuthenticator/CookieAuthenticationHandler.php b/src/Security/MemberAuthenticator/CookieAuthenticationHandler.php
index 2ac9ddd9fdc..8f71d503d45 100644
--- a/src/Security/MemberAuthenticator/CookieAuthenticationHandler.php
+++ b/src/Security/MemberAuthenticator/CookieAuthenticationHandler.php
@@ -203,7 +203,7 @@ public function authenticateRequest(HTTPRequest $request)
      * @param bool $persistent
      * @param HTTPRequest $request
      */
-    public function logIn(Member $member, $persistent = false, HTTPRequest $request = null)
+    public function logIn(Member $member, $persistent = false, ?HTTPRequest $request = null)
     {
         // Cleans up any potential previous hash for this member on this device
         if ($alcDevice = Cookie::get($this->getDeviceCookieName())) {
@@ -243,7 +243,7 @@ public function logIn(Member $member, $persistent = false, HTTPRequest $request
     /**
      * @param HTTPRequest $request
      */
-    public function logOut(HTTPRequest $request = null)
+    public function logOut(?HTTPRequest $request = null)
     {
         $member = Security::getCurrentUser();
         if ($member) {
diff --git a/src/Security/MemberAuthenticator/LoginHandler.php b/src/Security/MemberAuthenticator/LoginHandler.php
index db672e11c46..69921db9f41 100644
--- a/src/Security/MemberAuthenticator/LoginHandler.php
+++ b/src/Security/MemberAuthenticator/LoginHandler.php
@@ -217,7 +217,7 @@ protected function redirectAfterSuccessfulLogin()
      * @return Member Returns the member object on successful authentication
      *                or NULL on failure.
      */
-    public function checkLogin($data, HTTPRequest $request, ValidationResult &$result = null)
+    public function checkLogin($data, HTTPRequest $request, ?ValidationResult &$result = null)
     {
         $member = $this->authenticator->authenticate($data, $request, $result);
         if ($member instanceof Member) {
diff --git a/src/Security/MemberAuthenticator/MemberAuthenticator.php b/src/Security/MemberAuthenticator/MemberAuthenticator.php
index 29ed27a17e8..531a164b639 100644
--- a/src/Security/MemberAuthenticator/MemberAuthenticator.php
+++ b/src/Security/MemberAuthenticator/MemberAuthenticator.php
@@ -31,7 +31,7 @@ public function supportedServices()
             | Authenticator::RESET_PASSWORD | Authenticator::CHECK_PASSWORD;
     }
 
-    public function authenticate(array $data, HTTPRequest $request, ValidationResult &$result = null)
+    public function authenticate(array $data, HTTPRequest $request, ?ValidationResult &$result = null)
     {
         // Find authenticated member
         if (class_exists(Versioned::class)) {
@@ -62,7 +62,7 @@ public function authenticate(array $data, HTTPRequest $request, ValidationResult
      * @param Member $member This third parameter is used in the CMSAuthenticator(s)
      * @return Member Found member, regardless of successful login
      */
-    protected function authenticateMember($data, ValidationResult &$result = null, Member $member = null)
+    protected function authenticateMember($data, ?ValidationResult &$result = null, ?Member $member = null)
     {
         $email = !empty($data['Email']) ? $data['Email'] : null;
         $result = $result ?: ValidationResult::create();
@@ -135,7 +135,7 @@ protected function authenticateMember($data, ValidationResult &$result = null, M
      * @param ValidationResult $result
      * @return ValidationResult
      */
-    public function checkPassword(Member $member, $password, ValidationResult &$result = null)
+    public function checkPassword(Member $member, $password, ?ValidationResult &$result = null)
     {
         // Check if allowed to login
         $result = $member->validateCanLogin($result);
diff --git a/src/Security/MemberAuthenticator/SessionAuthenticationHandler.php b/src/Security/MemberAuthenticator/SessionAuthenticationHandler.php
index 252bb749315..8d8e5ff69af 100644
--- a/src/Security/MemberAuthenticator/SessionAuthenticationHandler.php
+++ b/src/Security/MemberAuthenticator/SessionAuthenticationHandler.php
@@ -71,7 +71,7 @@ public function authenticateRequest(HTTPRequest $request)
      * @param bool $persistent
      * @param HTTPRequest $request
      */
-    public function logIn(Member $member, $persistent = false, HTTPRequest $request = null)
+    public function logIn(Member $member, $persistent = false, ?HTTPRequest $request = null)
     {
         static::regenerateSessionId();
         $request = $request ?: Controller::curr()->getRequest();
@@ -116,7 +116,7 @@ protected static function regenerateSessionId()
     /**
      * @param HTTPRequest $request
      */
-    public function logOut(HTTPRequest $request = null)
+    public function logOut(?HTTPRequest $request = null)
     {
         $request = $request ?: Controller::curr()->getRequest();
         $request->getSession()->destroy(true, $request);
diff --git a/src/Security/PermissionChecker.php b/src/Security/PermissionChecker.php
index 0c1e0b99944..16be55d37c5 100644
--- a/src/Security/PermissionChecker.php
+++ b/src/Security/PermissionChecker.php
@@ -17,7 +17,7 @@ interface PermissionChecker
      * @return array A map where the IDs are keys and the values are
      * booleans stating whether the given object can be edited
      */
-    public function canEditMultiple($ids, Member $member = null, $useCached = true);
+    public function canEditMultiple($ids, ?Member $member = null, $useCached = true);
 
     /**
      * Get the canView information for a number of objects
@@ -27,7 +27,7 @@ public function canEditMultiple($ids, Member $member = null, $useCached = true);
      * @param bool $useCached
      * @return mixed
      */
-    public function canViewMultiple($ids, Member $member = null, $useCached = true);
+    public function canViewMultiple($ids, ?Member $member = null, $useCached = true);
 
     /**
      * Get the 'can edit' information for a number of SiteTree pages.
@@ -37,7 +37,7 @@ public function canViewMultiple($ids, Member $member = null, $useCached = true);
      * @param bool $useCached Return values from the permission cache if they exist
      * @return array
      */
-    public function canDeleteMultiple($ids, Member $member = null, $useCached = true);
+    public function canDeleteMultiple($ids, ?Member $member = null, $useCached = true);
 
     /**
      * Check delete permission for a single record ID
@@ -46,7 +46,7 @@ public function canDeleteMultiple($ids, Member $member = null, $useCached = true
      * @param Member $member
      * @return bool
      */
-    public function canDelete($id, Member $member = null);
+    public function canDelete($id, ?Member $member = null);
 
     /**
      * Check edit permission for a single record ID
@@ -55,7 +55,7 @@ public function canDelete($id, Member $member = null);
      * @param Member $member
      * @return bool
      */
-    public function canEdit($id, Member $member = null);
+    public function canEdit($id, ?Member $member = null);
 
     /**
      * Check view permission for a single record ID
@@ -64,5 +64,5 @@ public function canEdit($id, Member $member = null);
      * @param Member $member
      * @return bool
      */
-    public function canView($id, Member $member = null);
+    public function canView($id, ?Member $member = null);
 }
diff --git a/src/Security/RequestAuthenticationHandler.php b/src/Security/RequestAuthenticationHandler.php
index 20db10a4db1..a2a49494112 100644
--- a/src/Security/RequestAuthenticationHandler.php
+++ b/src/Security/RequestAuthenticationHandler.php
@@ -54,7 +54,7 @@ public function authenticateRequest(HTTPRequest $request)
      * @param bool $persistent
      * @param HTTPRequest $request
      */
-    public function logIn(Member $member, $persistent = false, HTTPRequest $request = null)
+    public function logIn(Member $member, $persistent = false, ?HTTPRequest $request = null)
     {
         $member->beforeMemberLoggedIn();
 
@@ -71,7 +71,7 @@ public function logIn(Member $member, $persistent = false, HTTPRequest $request
      *
      * @param HTTPRequest $request
      */
-    public function logOut(HTTPRequest $request = null)
+    public function logOut(?HTTPRequest $request = null)
     {
         $member = Security::getCurrentUser();
         if ($member) {
diff --git a/src/View/SSViewer.php b/src/View/SSViewer.php
index 92d28f8843f..915fcc94aa3 100644
--- a/src/View/SSViewer.php
+++ b/src/View/SSViewer.php
@@ -190,7 +190,7 @@ class SSViewer implements Flushable
      *  </code>
      * @param TemplateParser $parser
      */
-    public function __construct($templates, TemplateParser $parser = null)
+    public function __construct($templates, ?TemplateParser $parser = null)
     {
         if ($parser) {
             Deprecation::noticeWithNoReplacment('5.4.0', 'The $parser parameter is deprecated and will be removed');
diff --git a/src/View/SSViewer_DataPresenter.php b/src/View/SSViewer_DataPresenter.php
index e09fe83f146..7f9ca631b48 100644
--- a/src/View/SSViewer_DataPresenter.php
+++ b/src/View/SSViewer_DataPresenter.php
@@ -62,9 +62,9 @@ class SSViewer_DataPresenter extends SSViewer_Scope
      */
     public function __construct(
         $item,
-        array $overlay = null,
-        array $underlay = null,
-        SSViewer_Scope $inheritedScope = null
+        ?array $overlay = null,
+        ?array $underlay = null,
+        ?SSViewer_Scope $inheritedScope = null
     ) {
         Deprecation::noticeWithNoReplacment('5.4.0', 'Will be merged into ' . SSViewer_Scope::class, Deprecation::SCOPE_CLASS);
         parent::__construct($item, $inheritedScope);
diff --git a/src/View/SSViewer_FromString.php b/src/View/SSViewer_FromString.php
index 23b808179e6..fcf9b450320 100644
--- a/src/View/SSViewer_FromString.php
+++ b/src/View/SSViewer_FromString.php
@@ -37,7 +37,7 @@ class SSViewer_FromString extends SSViewer
      * @param string $content
      * @param TemplateParser $parser
      */
-    public function __construct($content, TemplateParser $parser = null)
+    public function __construct($content, ?TemplateParser $parser = null)
     {
         Deprecation::noticeWithNoReplacment(
             '5.4.0',
diff --git a/src/View/SSViewer_Scope.php b/src/View/SSViewer_Scope.php
index f6f46b4cb54..8862b1ecf05 100644
--- a/src/View/SSViewer_Scope.php
+++ b/src/View/SSViewer_Scope.php
@@ -114,7 +114,7 @@ class SSViewer_Scope
      * @var object $item
      * @var SSViewer_Scope $inheritedScope
      */
-    public function __construct($item, SSViewer_Scope $inheritedScope = null)
+    public function __construct($item, ?SSViewer_Scope $inheritedScope = null)
     {
         Deprecation::noticeWithNoReplacment(
             '5.4.0',
diff --git a/src/View/ThemeManifest.php b/src/View/ThemeManifest.php
index 402ac4aa6b5..9b2303c7487 100644
--- a/src/View/ThemeManifest.php
+++ b/src/View/ThemeManifest.php
@@ -63,7 +63,7 @@ class ThemeManifest implements ThemeList
      * @param string $project Path to application code
      * @param CacheFactory $cacheFactory Cache factory to generate backend cache with
      */
-    public function __construct($base, $project = null, CacheFactory $cacheFactory = null)
+    public function __construct($base, $project = null, ?CacheFactory $cacheFactory = null)
     {
         $this->base = $base;
         $this->project = $project;
diff --git a/src/i18n/TextCollection/i18nTextCollector.php b/src/i18n/TextCollection/i18nTextCollector.php
index 7bc44598b56..3384990de34 100644
--- a/src/i18n/TextCollection/i18nTextCollector.php
+++ b/src/i18n/TextCollection/i18nTextCollector.php
@@ -927,7 +927,7 @@ public function collectFromTemplate($content, $fileName, Module $module, &$parse
      * @param Module $module
      * @return array
      */
-    public function collectFromEntityProviders($filePath, Module $module = null)
+    public function collectFromEntityProviders($filePath, ?Module $module = null)
     {
         $entities = [];
         $classes = ClassInfo::classes_for_file($filePath);
diff --git a/tests/php/Control/HttpRequestMockBuilder.php b/tests/php/Control/HttpRequestMockBuilder.php
index ffbd2cbfcfe..5c3e0e72d35 100644
--- a/tests/php/Control/HttpRequestMockBuilder.php
+++ b/tests/php/Control/HttpRequestMockBuilder.php
@@ -18,7 +18,7 @@ trait HttpRequestMockBuilder
      *
      * @return HTTPRequest
      */
-    public function buildRequestMock($url, $getVars = [], $postVars = [], $method = null, Session $session = null)
+    public function buildRequestMock($url, $getVars = [], $postVars = [], $method = null, ?Session $session = null)
     {
         if (is_null($session)) {
             $session = new Session([]);
diff --git a/tests/php/Forms/FormFactoryTest/EditFormFactory.php b/tests/php/Forms/FormFactoryTest/EditFormFactory.php
index 6ada58c98fd..9bf2c8ddb2a 100644
--- a/tests/php/Forms/FormFactoryTest/EditFormFactory.php
+++ b/tests/php/Forms/FormFactoryTest/EditFormFactory.php
@@ -18,7 +18,7 @@ class EditFormFactory extends DefaultFormFactory
         ControllerExtension::class
     ];
 
-    protected function getFormFields(RequestHandler $controller = null, $name, $context = [])
+    protected function getFormFields(?RequestHandler $controller = null, $name, $context = [])
     {
         $fields = new FieldList(
             new HiddenField('ID'),
@@ -28,7 +28,7 @@ protected function getFormFields(RequestHandler $controller = null, $name, $cont
         return $fields;
     }
 
-    protected function getFormActions(RequestHandler $controller = null, $name, $context = [])
+    protected function getFormActions(?RequestHandler $controller = null, $name, $context = [])
     {
         $actions = new FieldList(
             new FormAction('save', 'Save')
diff --git a/tests/php/Security/InheritedPermissionsTest/TestDefaultPermissionChecker.php b/tests/php/Security/InheritedPermissionsTest/TestDefaultPermissionChecker.php
index c82407c1133..2b07f3ada6f 100644
--- a/tests/php/Security/InheritedPermissionsTest/TestDefaultPermissionChecker.php
+++ b/tests/php/Security/InheritedPermissionsTest/TestDefaultPermissionChecker.php
@@ -17,7 +17,7 @@ class TestDefaultPermissionChecker implements DefaultPermissionChecker
      * @param Member $member
      * @return bool
      */
-    public function canEdit(Member $member = null)
+    public function canEdit(?Member $member = null)
     {
         return $this->canEdit;
     }
@@ -28,7 +28,7 @@ public function canEdit(Member $member = null)
      * @param Member $member
      * @return bool
      */
-    public function canView(Member $member = null)
+    public function canView(?Member $member = null)
     {
         return $this->canView;
     }
@@ -39,7 +39,7 @@ public function canView(Member $member = null)
      * @param Member $member
      * @return bool
      */
-    public function canDelete(Member $member = null)
+    public function canDelete(?Member $member = null)
     {
         return $this->canEdit;
     }
@@ -50,7 +50,7 @@ public function canDelete(Member $member = null)
      * @param Member $member
      * @return bool
      */
-    public function canCreate(Member $member = null)
+    public function canCreate(?Member $member = null)
     {
         return $this->canEdit;
     }