diff --git a/main/gradebook/lib/be/category.class.php b/main/gradebook/lib/be/category.class.php
index f7b2783872..8963e5e28f 100755
--- a/main/gradebook/lib/be/category.class.php
+++ b/main/gradebook/lib/be/category.class.php
@@ -2165,7 +2165,7 @@ class Category implements GradebookItem
      * @param int $user_id
      * @param bool $sendNotification
      *
-     * @return bool|string
+     * @return array
      */
     public static function generateUserCertificate(
         $category_id,
@@ -2538,7 +2538,7 @@ class Category implements GradebookItem
      * @param float $score The achieved score
      * @param int $userId The user id
      * @param int $categoryId The gradebook category
-     * @return false|string The insert id
+     * @return int The insert id
      */
     public static function registerCurrentScore($score, $userId, $categoryId)
     {
diff --git a/main/gradebook/lib/be/evaluation.class.php b/main/gradebook/lib/be/evaluation.class.php
index d882133a4e..f786e5ed3d 100755
--- a/main/gradebook/lib/be/evaluation.class.php
+++ b/main/gradebook/lib/be/evaluation.class.php
@@ -456,7 +456,7 @@ class Evaluation implements GradebookItem
 
     /**
      * Check if an evaluation name (with the same parent category) already exists
-     * @param $name name to check (if not given, the name property of this object will be checked)
+     * @param string $name to check (if not given, the name property of this object will be checked)
      * @param $parent parent category
      * @return bool
      */
diff --git a/main/gradebook/lib/fe/displaygradebook.php b/main/gradebook/lib/fe/displaygradebook.php
index 72c240daf3..f901e18642 100755
--- a/main/gradebook/lib/fe/displaygradebook.php
+++ b/main/gradebook/lib/fe/displaygradebook.php
@@ -242,14 +242,17 @@ class DisplayGradebook
      * Displays the header for the gradebook containing the navigation tree and links
      * @param Category $catobj
      * @param int $showtree '1' will show the browse tree and naviation buttons
+     * @param $selectcat
      * @param boolean $is_course_admin
      * @param boolean $is_platform_admin
-     * @param boolean Whether to show or not the link to add a new qualification
+     * @param bool $simple_search_form
+     * @param boolean $show_add_qualification Whether to show or not the link to add a new qualification
      * (we hide it in case of the course-embedded tool where we have only one
-     * calification per course or session)
-     * @param boolean Whether to show or not the link to add a new item inside
+     * per course or session)
+     * @param boolean $show_add_link Whether to show or not the link to add a new item inside
      * the qualification (we hide it in case of the course-embedded tool
-     * where we have only one calification per course or session)
+     * where we have only one qualification per course or session)
+     * @param array $certificateLinkInfo
      * @return void Everything is printed on screen upon closing
      */
     public static function header(
@@ -261,7 +264,7 @@ class DisplayGradebook
         $simple_search_form,
         $show_add_qualification = true,
         $show_add_link = true,
-        $certificateLinkInfo = null
+        $certificateLinkInfo = []
     ) {
         $userId = api_get_user_id();
         $courseId = api_get_course_int_id();
@@ -284,7 +287,6 @@ class DisplayGradebook
         $message_resource = $objcat->show_message_resource_delete($course_id);
         $grade_model_id = $catobj->get_grade_model_id();
         $header = null;
-
         if (isset($catobj) && !empty($catobj)) {
             $categories = Category::load(
                 null,