diff --git a/main/exercise/Annotation.php b/main/exercise/Annotation.php
index 0fc67b81697..43b46f0b70b 100644
--- a/main/exercise/Annotation.php
+++ b/main/exercise/Annotation.php
@@ -127,7 +127,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = [])
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $score['revised'] = $this->isQuestionWaitingReview($score);
 
diff --git a/main/exercise/Draggable.php b/main/exercise/Draggable.php
index 2b307d9c116..bc08cde916c 100644
--- a/main/exercise/Draggable.php
+++ b/main/exercise/Draggable.php
@@ -210,7 +210,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';
diff --git a/main/exercise/MatchingDraggable.php b/main/exercise/MatchingDraggable.php
index 7affd9a6f67..a19838e12f4 100644
--- a/main/exercise/MatchingDraggable.php
+++ b/main/exercise/MatchingDraggable.php
@@ -260,7 +260,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="matching '.$this->question_table_class.'"><tr>';
diff --git a/main/exercise/MultipleAnswerTrueFalseDegreeCertainty.php b/main/exercise/MultipleAnswerTrueFalseDegreeCertainty.php
index beb21654dc8..ec06be784c9 100644
--- a/main/exercise/MultipleAnswerTrueFalseDegreeCertainty.php
+++ b/main/exercise/MultipleAnswerTrueFalseDegreeCertainty.php
@@ -301,15 +301,9 @@ public function processAnswersCreation($form, $exercise)
     }
 
     /**
-     * Show result table headers.
-     *
-     * @param Exercise $exercise
-     * @param int      $counter
-     * @param float    $score
-     *
-     * @return string|null
+     * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'
diff --git a/main/exercise/UniqueAnswerImage.php b/main/exercise/UniqueAnswerImage.php
index b8a3f42470a..849cd8ec8b7 100644
--- a/main/exercise/UniqueAnswerImage.php
+++ b/main/exercise/UniqueAnswerImage.php
@@ -371,13 +371,9 @@ public function processAnswersCreation($form, $exercise)
     }
 
     /**
-     * @param Exercise $exercise
-     * @param null     $counter
-     * @param null     $score
-     *
-     * @return string
+     * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         if ($exercise->showExpectedChoice()) {
             $header = '<table class="'.$this->question_table_class.'">
diff --git a/main/exercise/calculated_answer.class.php b/main/exercise/calculated_answer.class.php
index de86b73e7cd..4df19a690a2 100644
--- a/main/exercise/calculated_answer.class.php
+++ b/main/exercise/calculated_answer.class.php
@@ -245,7 +245,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';
diff --git a/main/exercise/fill_blanks.class.php b/main/exercise/fill_blanks.class.php
index 2ec7f259345..c280028f397 100755
--- a/main/exercise/fill_blanks.class.php
+++ b/main/exercise/fill_blanks.class.php
@@ -484,7 +484,7 @@ function ($matches) use ($blankStartSeparator, $blankEndSeparator) {
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'">
diff --git a/main/exercise/freeanswer.class.php b/main/exercise/freeanswer.class.php
index bedd15027bf..4306d196b68 100755
--- a/main/exercise/freeanswer.class.php
+++ b/main/exercise/freeanswer.class.php
@@ -55,7 +55,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = [])
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $score['revised'] = $this->isQuestionWaitingReview($score);
         $header = parent::return_header($exercise, $counter, $score);
diff --git a/main/exercise/global_multiple_answer.class.php b/main/exercise/global_multiple_answer.class.php
index 816c4a979f9..390ea1d4b74 100755
--- a/main/exercise/global_multiple_answer.class.php
+++ b/main/exercise/global_multiple_answer.class.php
@@ -261,11 +261,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header(
-        $exercise,
-        $counter = null,
-        $score = null
-    ) {
+    public function return_header(Exercise $exercise, $counter = null, $score = []) {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';
 
diff --git a/main/exercise/matching.class.php b/main/exercise/matching.class.php
index 37f86631833..34e4af96f5e 100755
--- a/main/exercise/matching.class.php
+++ b/main/exercise/matching.class.php
@@ -280,7 +280,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'">';
diff --git a/main/exercise/multiple_answer.class.php b/main/exercise/multiple_answer.class.php
index 9e5ea26490c..94b6875c3e2 100755
--- a/main/exercise/multiple_answer.class.php
+++ b/main/exercise/multiple_answer.class.php
@@ -229,7 +229,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';
diff --git a/main/exercise/multiple_answer_combination.class.php b/main/exercise/multiple_answer_combination.class.php
index 61b6cf5ad3e..92be1521fec 100755
--- a/main/exercise/multiple_answer_combination.class.php
+++ b/main/exercise/multiple_answer_combination.class.php
@@ -227,7 +227,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';
diff --git a/main/exercise/multiple_answer_true_false.class.php b/main/exercise/multiple_answer_true_false.class.php
index ad95d7901da..0b17b76687a 100755
--- a/main/exercise/multiple_answer_true_false.class.php
+++ b/main/exercise/multiple_answer_true_false.class.php
@@ -308,7 +308,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';
diff --git a/main/exercise/oral_expression.class.php b/main/exercise/oral_expression.class.php
index 185035cc06b..692fe4f0783 100755
--- a/main/exercise/oral_expression.class.php
+++ b/main/exercise/oral_expression.class.php
@@ -67,7 +67,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $score['revised'] = $this->isQuestionWaitingReview($score);
         $header = parent::return_header($exercise, $counter, $score);
diff --git a/main/exercise/unique_answer.class.php b/main/exercise/unique_answer.class.php
index c0dea563946..683c6751e7a 100755
--- a/main/exercise/unique_answer.class.php
+++ b/main/exercise/unique_answer.class.php
@@ -408,11 +408,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header(
-        $exercise,
-        $counter = null,
-        $score = null
-    ) {
+    public function return_header(Exercise $exercise, $counter = null, $score = []) {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';
 
diff --git a/main/exercise/unique_answer_no_option.class.php b/main/exercise/unique_answer_no_option.class.php
index ec96ae1ff3e..8d8fb56be41 100755
--- a/main/exercise/unique_answer_no_option.class.php
+++ b/main/exercise/unique_answer_no_option.class.php
@@ -399,7 +399,7 @@ public function processAnswersCreation($form, $exercise)
     /**
      * {@inheritdoc}
      */
-    public function return_header($exercise, $counter = null, $score = null)
+    public function return_header(Exercise $exercise, $counter = null, $score = [])
     {
         $header = parent::return_header($exercise, $counter, $score);
         $header .= '<table class="'.$this->question_table_class.'"><tr>';