diff --git a/src/Lti1p1Key.php b/src/Lti1p1Key.php
index 7bd5026e..b67a699d 100644
--- a/src/Lti1p1Key.php
+++ b/src/Lti1p1Key.php
@@ -12,7 +12,7 @@ class Lti1p1Key
     private $key;
     private $secret;
 
-    public function __construct(array $key = null)
+    public function __construct(?array $key = null)
     {
         $this->key = $key['key'] ?? null;
         $this->secret = $key['secret'] ?? null;
diff --git a/src/LtiAbstractService.php b/src/LtiAbstractService.php
index 0f33d3ad..8f08dcfa 100644
--- a/src/LtiAbstractService.php
+++ b/src/LtiAbstractService.php
@@ -52,7 +52,7 @@ protected function makeServiceRequest(IServiceRequest $request): array
         );
     }
 
-    protected function getAll(IServiceRequest $request, string $key = null): array
+    protected function getAll(IServiceRequest $request, ?string $key = null): array
     {
         return $this->serviceConnector->getAll(
             $this->registration,
diff --git a/src/LtiAssignmentsGradesService.php b/src/LtiAssignmentsGradesService.php
index 52035ecb..9700684e 100644
--- a/src/LtiAssignmentsGradesService.php
+++ b/src/LtiAssignmentsGradesService.php
@@ -28,7 +28,7 @@ public function getResourceLaunchLineItem(): ?LtiLineitem
         return LtiLineitem::new()->setId($serviceData['lineitem']);
     }
 
-    public function putGrade(LtiGrade $grade, LtiLineitem $lineitem = null)
+    public function putGrade(LtiGrade $grade, ?LtiLineitem $lineitem = null)
     {
         $this->validateScopes([LtiConstants::AGS_SCOPE_SCORE]);
 
@@ -107,7 +107,7 @@ public function findOrCreateLineitem(LtiLineitem $newLineItem): LtiLineitem
         return $this->findLineItem($newLineItem) ?? $this->createLineitem($newLineItem);
     }
 
-    public function getGrades(LtiLineitem $lineitem = null)
+    public function getGrades(?LtiLineitem $lineitem = null)
     {
         $lineitem = $this->ensureLineItemExists($lineitem);
         $resultsUrl = $this->appendLineItemPath($lineitem, '/results');
@@ -159,7 +159,7 @@ public function getLineItem(string $url): LtiLineitem
         return new LtiLineitem($response);
     }
 
-    private function ensureLineItemExists(LtiLineitem $lineitem = null): LtiLineitem
+    private function ensureLineItemExists(?LtiLineitem $lineitem = null): LtiLineitem
     {
         // If no line item is passed in, attempt to use the one associated with
         // this launch.
diff --git a/src/LtiDeepLinkDateTimeInterval.php b/src/LtiDeepLinkDateTimeInterval.php
index b26c6687..8639c4aa 100644
--- a/src/LtiDeepLinkDateTimeInterval.php
+++ b/src/LtiDeepLinkDateTimeInterval.php
@@ -9,7 +9,7 @@ class LtiDeepLinkDateTimeInterval
     private ?DateTime $start;
     private ?DateTime $end;
 
-    public function __construct(DateTime $start = null, DateTime $end = null)
+    public function __construct(?DateTime $start = null, ?DateTime $end = null)
     {
         if ($start !== null && $end !== null && $end < $start) {
             throw new LtiException('Interval start time cannot be greater than end time');
diff --git a/src/LtiDeepLinkResourceIframe.php b/src/LtiDeepLinkResourceIframe.php
index 3346c31a..de60ec3f 100644
--- a/src/LtiDeepLinkResourceIframe.php
+++ b/src/LtiDeepLinkResourceIframe.php
@@ -8,7 +8,7 @@ class LtiDeepLinkResourceIframe
     private ?int $height;
     private ?string $src;
 
-    public function __construct(int $width = null, int $height = null, string $src = null)
+    public function __construct(?int $width = null, ?int $height = null, ?string $src = null)
     {
         $this->width = $width ?? null;
         $this->height = $height ?? null;
diff --git a/src/LtiDeepLinkResourceWindow.php b/src/LtiDeepLinkResourceWindow.php
index 323d706c..194f32a7 100644
--- a/src/LtiDeepLinkResourceWindow.php
+++ b/src/LtiDeepLinkResourceWindow.php
@@ -9,7 +9,7 @@ class LtiDeepLinkResourceWindow
     private ?int $height;
     private ?string $window_features;
 
-    public function __construct(string $targetName = null, int $width = null, int $height = null, string $windowFeatures = null)
+    public function __construct(?string $targetName = null, ?int $width = null, ?int $height = null, ?string $windowFeatures = null)
     {
         $this->target_name = $targetName ?? null;
         $this->width = $width ?? null;
diff --git a/src/LtiGrade.php b/src/LtiGrade.php
index bca75be8..d3f0e18a 100644
--- a/src/LtiGrade.php
+++ b/src/LtiGrade.php
@@ -14,7 +14,7 @@ class LtiGrade
     private $submission_review;
     private $canvas_extension;
 
-    public function __construct(array $grade = null)
+    public function __construct(?array $grade = null)
     {
         $this->score_given = $grade['scoreGiven'] ?? null;
         $this->score_maximum = $grade['scoreMaximum'] ?? null;
diff --git a/src/LtiGradeSubmissionReview.php b/src/LtiGradeSubmissionReview.php
index a185930f..335590a7 100644
--- a/src/LtiGradeSubmissionReview.php
+++ b/src/LtiGradeSubmissionReview.php
@@ -9,7 +9,7 @@ class LtiGradeSubmissionReview
     private $url;
     private $custom;
 
-    public function __construct(array $gradeSubmission = null)
+    public function __construct(?array $gradeSubmission = null)
     {
         $this->reviewable_status = $gradeSubmission['reviewableStatus'] ?? null;
         $this->label = $gradeSubmission['label'] ?? null;
diff --git a/src/LtiLineitem.php b/src/LtiLineitem.php
index 9492c1a6..4223dedc 100644
--- a/src/LtiLineitem.php
+++ b/src/LtiLineitem.php
@@ -14,7 +14,7 @@ class LtiLineitem
     private $end_date_time;
     private ?bool $grades_released;
 
-    public function __construct(array $lineitem = null)
+    public function __construct(?array $lineitem = null)
     {
         $this->id = $lineitem['id'] ?? null;
         $this->score_maximum = $lineitem['scoreMaximum'] ?? null;
diff --git a/src/LtiMessageLaunch.php b/src/LtiMessageLaunch.php
index 2f15c69e..d2e00a7e 100644
--- a/src/LtiMessageLaunch.php
+++ b/src/LtiMessageLaunch.php
@@ -80,9 +80,9 @@ class LtiMessageLaunch
      */
     public function __construct(
         IDatabase $database,
-        ICache $cache = null,
-        ICookie $cookie = null,
-        ILtiServiceConnector $serviceConnector = null
+        ?ICache $cache = null,
+        ?ICookie $cookie = null,
+        ?ILtiServiceConnector $serviceConnector = null
     ) {
         $this->db = $database;
 
@@ -98,9 +98,9 @@ public function __construct(
      */
     public static function new(
         IDatabase $database,
-        ICache $cache = null,
-        ICookie $cookie = null,
-        ILtiServiceConnector $serviceConnector = null
+        ?ICache $cache = null,
+        ?ICookie $cookie = null,
+        ?ILtiServiceConnector $serviceConnector = null
     ) {
         return new LtiMessageLaunch($database, $cache, $cookie, $serviceConnector);
     }
@@ -118,8 +118,8 @@ public static function new(
     public static function fromCache(
         $launch_id,
         IDatabase $database,
-        ICache $cache = null,
-        ILtiServiceConnector $serviceConnector = null
+        ?ICache $cache = null,
+        ?ILtiServiceConnector $serviceConnector = null
     ) {
         // @todo: Fix the null here on the next major version
         $new = new LtiMessageLaunch($database, $cache, null, $serviceConnector);
@@ -153,7 +153,7 @@ public function initialize(array $request)
      *
      * @throws LtiException Will throw an LtiException if validation fails
      */
-    public function validate(array $request = null)
+    public function validate(?array $request = null)
     {
         // @TODO: Remove this on the next major release.
         if (!isset($this->request)) {
@@ -337,7 +337,7 @@ public function getLaunchId()
         return $this->launch_id;
     }
 
-    public static function getMissingRegistrationErrorMsg(string $issuerUrl, string $clientId = null): string
+    public static function getMissingRegistrationErrorMsg(string $issuerUrl, ?string $clientId = null): string
     {
         // Guard against client ID being null
         if (!isset($clientId)) {
diff --git a/src/LtiOidcLogin.php b/src/LtiOidcLogin.php
index f6582107..5c1d7048 100644
--- a/src/LtiOidcLogin.php
+++ b/src/LtiOidcLogin.php
@@ -24,7 +24,7 @@ class LtiOidcLogin
      * @param  ICache  $cache    instance of the Cache interface used to loading and storing launches
      * @param  ICookie  $cookie   instance of the Cookie interface used to set and read cookies
      */
-    public function __construct(IDatabase $database, ICache $cache = null, ICookie $cookie = null)
+    public function __construct(IDatabase $database, ?ICache $cache = null, ?ICookie $cookie = null)
     {
         $this->db = $database;
         $this->cache = $cache;
@@ -34,7 +34,7 @@ public function __construct(IDatabase $database, ICache $cache = null, ICookie $
     /**
      * Static function to allow for method chaining without having to assign to a variable first.
      */
-    public static function new(IDatabase $database, ICache $cache = null, ICookie $cookie = null)
+    public static function new(IDatabase $database, ?ICache $cache = null, ?ICookie $cookie = null)
     {
         return new LtiOidcLogin($database, $cache, $cookie);
     }
@@ -46,7 +46,7 @@ public static function new(IDatabase $database, ICache $cache = null, ICookie $c
      * @param  array  $request    An array of request parameters. If not set will default to $_REQUEST.
      * @return Redirect returns a redirect object containing the fully formed OIDC login URL
      */
-    public function doOidcLoginRedirect($launchUrl, array $request = null)
+    public function doOidcLoginRedirect($launchUrl, ?array $request = null)
     {
         // @todo remove this in v6.0
         if ($request === null) {
diff --git a/src/LtiServiceConnector.php b/src/LtiServiceConnector.php
index 9cff50d3..16bb9478 100644
--- a/src/LtiServiceConnector.php
+++ b/src/LtiServiceConnector.php
@@ -154,7 +154,7 @@ public function getAll(
         ILtiRegistration $registration,
         array $scopes,
         IServiceRequest $request,
-        string $key = null
+        ?string $key = null
     ): array {
         if ($request->getMethod() !== ServiceRequest::METHOD_GET) {
             throw new Exception('An invalid method was specified by an LTI service requesting all items.');
diff --git a/src/Redirect.php b/src/Redirect.php
index f90f6961..fa4ba87a 100644
--- a/src/Redirect.php
+++ b/src/Redirect.php
@@ -10,7 +10,7 @@ class Redirect
     private $referer_query;
     private static $CAN_302_COOKIE = 'LTI_302_Redirect';
 
-    public function __construct(string $location, string $referer_query = null)
+    public function __construct(string $location, ?string $referer_query = null)
     {
         $this->location = $location;
         $this->referer_query = $referer_query;
diff --git a/tests/Certification/Lti13CertificationTest.php b/tests/Certification/Lti13CertificationTest.php
index 3c094727..14575d83 100644
--- a/tests/Certification/Lti13CertificationTest.php
+++ b/tests/Certification/Lti13CertificationTest.php
@@ -581,7 +581,7 @@ public function testValidCertificationCases()
         $this->assertEquals($casesCount, $testedCases);
     }
 
-    private function launch($payload, IDatabase $db = null)
+    private function launch($payload, ?IDatabase $db = null)
     {
         $db = $db ?? $this->db;