JavaScript error formChild is null on completion page

[leonstr]

Steps to reproduce issue

1. Create a course, enrol a teacher and student.
2. As the teacher:
3. Add a Questionnaire to the course.
4. Click Add questions and add a question.
5. As the student click on the Questionnaire on the course page, then click Answer the questions....
6. As the student answer the question and click Submit questionnaire.

Expected results

No errors in browser console.

Actual results

Error on browser console: Uncaught TypeError: formChild is null.

Environment

This error occurs in Moodle 4.0, 4.1 and 4.2 with mod_questionnaire 2022092202. It occurs with Moodle 4.3.3 and later, and Moodle 4.4 with PR #584 (needed to get the JavaScript to run at all).

[leonstr]

PR #595 has a proposed fix for this.

[mchurchward]

Fixed in #595