Minor - fix behat test

public/main/gradebook/lib/be/category.class.php

@@ -45,7 +45,7 @@ class Category implements GradebookItem
     {
         $this->id = 0;
         $this->name = null;
-        $this->description = null;
+        $this->description = '';
         $this->user_id = 0;
         $this->course_code = '';
         $this->courseId = 0;

src/CoreBundle/Entity/GradebookCategory.php

@@ -211,7 +211,7 @@ class GradebookCategory
     /**
      * Set description.
      */
-    public function setDescription(string $description): self
+    public function setDescription(?string $description): self
     {
         $this->description = $description;
 

src/CoreBundle/Entity/GradebookEvaluation.php

@@ -134,9 +134,6 @@ class GradebookEvaluation
      */
     protected $userScoreList;
 
-    /**
-     * GradebookEvaluation constructor.
-     */
     public function __construct()
     {
         $this->locked = 0;
@@ -168,12 +165,8 @@ class GradebookEvaluation
 
     /**
      * Set description.
-     *
-     * @param string $description
-     *
-     * @return GradebookEvaluation
      */
-    public function setDescription($description)
+    public function setDescription(?string $description): self
     {
         $this->description = $description;