When I navigate to an assignment in a course and click the Grade button, I get a broken page.

Steps to reproduce:

1. Log in as a Site Administrator.
2. Create a new course called Test Assignment.
3. Enrol yourself as a Teacher and a Student
4. Turn editing on.
5. Add an assignment activity.
6. Assignment name: My Test Assignment.
7. Submission type: Make sure Online Text is checked.
8. Click "Save and Display" button.
9. Click "Add a submission" button.
10. In the "Online text" field, just put the word "test".
11. Click "Save changes" button.
12. Click the "Grade" button.

This is what you end up seeing:

This is what I expected to see (screenshot from Moodle 4.3):