no feedback in quiz review when grade is negative (using CBM)

1. Create a quiz set to Deferred feedback with CBM behaviour, and some overall feedback, for example Feedback: Good; Grade boundary 50%; Feedback: Bad.
2. Add one question, a T/F question with right-answer true.
3. Attempt the quiz as a student. Give the answer false, and say that you are very sure you are right.
4. Submit all and finish. You should get a score of -2 for the question, so the overall attempt score should also be negative.
5. Verify that the Overall feedback is displayed at the top of the review page, and also on the view.php page when you click finish review.
6. Log in as teacher, and verify that the overall feedback is also shown in the Responses report.

in /mod/quiz/locallib.php (line 346) I added the following hack:

function quiz_feedback_for_grade($grade, $quiz, $context) {
global $DB;

if (is_null($grade))

/*****

• hack
• set $grade to 0 if $grade is negative so that students with a negative grade do get feedback
  *****/
  $grade = max(0, $grade);
  /*****
• end hack
  *****/

This however, does not enable a specific feedback for negative grades