diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7fa8c53d..d09e13ea 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,15 +30,15 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - php: '8.4'
+            moodle-branch: 'MOODLE_500_STABLE'
+            database: 'pgsql'
           - php: '8.3'
-            moodle-branch: 'MOODLE_405_STABLE'
+            moodle-branch: 'MOODLE_500_STABLE'
             database: 'mariadb'
           - php: '8.2'
-            moodle-branch: 'MOODLE_405_STABLE'
+            moodle-branch: 'MOODLE_500_STABLE'
             database: 'pgsql'
-          - php: '8.1'
-            moodle-branch: 'MOODLE_404_STABLE'
-            database: 'mariadb'
 
     steps:
       - name: Checkout
diff --git a/classes/question/question.php b/classes/question/question.php
index ed191496..2c96a833 100644
--- a/classes/question/question.php
+++ b/classes/question/question.php
@@ -653,9 +653,9 @@ public function update($questionrecord = null, $updatechoices = true) {
      * Add the question to the database from supplied arguments.
      * @param \stdClass $questionrecord The required data for adding the question.
      * @param array $choicerecords An array of choice records with 'content' and 'value' properties.
-     * @param boolean $calcposition Whether or not to calculate the next available position in the survey.
+     * @param bool|null $calcposition Whether or not to calculate the next available position in the survey.
      */
-    public function add($questionrecord, array $choicerecords = null, $calcposition = true) {
+    public function add($questionrecord, ?array $choicerecords = null, ?bool $calcposition = true) {
         global $DB;
 
         // Create new question.
diff --git a/classes/question/rate.php b/classes/question/rate.php
index 8e0117da..b21bfc55 100644
--- a/classes/question/rate.php
+++ b/classes/question/rate.php
@@ -1026,9 +1026,9 @@ public function insert_nameddegrees(array $nameddegrees) {
      * Helper function used to move existing named degree choices for the specified question from the "quest_choice" table to the
      * "question" table.
      * @param int $qid
-     * @param null|\stdClass $questionrec
+     * @param \stdClass|null $questionrec
      */
-    public static function move_nameddegree_choices(int $qid = 0, \stdClass $questionrec = null) {
+    public static function move_nameddegree_choices(int $qid = 0, ?\stdClass $questionrec = null) {
         global $DB;
 
         if ($qid !== 0) {
@@ -1079,7 +1079,7 @@ public static function move_nameddegree_choices(int $qid = 0, \stdClass $questio
      * questionnaire before '2018110103'.
      * @param int|null $surveyid
      */
-    public static function move_all_nameddegree_choices(int $surveyid = null) {
+    public static function move_all_nameddegree_choices(?int $surveyid = null) {
         global $DB;
 
         // This operation might take a while. Cancel PHP timeouts for this.
diff --git a/classes/responsetype/responsetype.php b/classes/responsetype/responsetype.php
index aa9c5dd2..1e879781 100644
--- a/classes/responsetype/responsetype.php
+++ b/classes/responsetype/responsetype.php
@@ -45,9 +45,9 @@ abstract class responsetype {
      * responsetype constructor.
      * @param \mod_questionnaire\question\question $question
      * @param int|null $responseid
-     * @param array $choices
+     * @param array|null $choices
      */
-    public function __construct(\mod_questionnaire\question\question $question, int $responseid = null, array $choices = []) {
+    public function __construct(\mod_questionnaire\question\question $question, ?int $responseid = null, ?array $choices = []) {
         $this->question = $question;
         $this->responseid = $responseid;
         $this->choices = $choices;
diff --git a/tests/behat/behat_mod_questionnaire.php b/tests/behat/behat_mod_questionnaire.php
index 57c97c58..39b47d51 100644
--- a/tests/behat/behat_mod_questionnaire.php
+++ b/tests/behat/behat_mod_questionnaire.php
@@ -418,7 +418,7 @@ private function add_response_data($qid, $sid) {
      *                         to replace with mapped values.
      * @return null
      */
-    private function add_data(array $data, $datatable, $mapvar = '', array $replvars = null) {
+    private function add_data(array $data, $datatable, $mapvar = '', ?array $replvars = null) {
         global $DB;
 
         if ($replvars === null) {
diff --git a/tests/custom_completion_test.php b/tests/custom_completion_test.php
index e46ce656..c266b8a5 100644
--- a/tests/custom_completion_test.php
+++ b/tests/custom_completion_test.php
@@ -51,7 +51,7 @@ class custom_completion_test extends \advanced_testcase {
      *
      * @return array[]
      */
-    public function get_state_provider(): array {
+    public static function get_state_provider(): array {
         return [
             'Undefined rule' => [
                 'somenonexistentrule', COMPLETION_DISABLED, false, null, coding_exception::class
@@ -178,7 +178,7 @@ public function test_is_defined() {
      *
      * @return array[]
      */
-    public function get_available_custom_rules_provider(): array {
+    public static function get_available_custom_rules_provider(): array {
         return [
             'Completion submit available' => [
                 COMPLETION_ENABLED, ['completionsubmit']
diff --git a/tests/generator/lib.php b/tests/generator/lib.php
index 447c5246..77b94a90 100644
--- a/tests/generator/lib.php
+++ b/tests/generator/lib.php
@@ -76,10 +76,10 @@ public function questionnaires() {
     /**
      * Create a questionnaire activity.
      * @param array $record Will be changed in this function.
-     * @param array $options
+     * @param array|null $options
      * @return questionnaire
      */
-    public function create_instance($record = null, array $options = null) {
+    public function create_instance($record = null, ?array $options = null) {
         $record = (object)(array)$record;
 
         $defaultquestionnairesettings = array(