Grade page is broken if submission other than PDF was deleted

Log in as a teacher in a course. Create an assignment with the following settings: Submission types File submissions Maximum number of uploaded files 2 (or more) Feedback types Annotate PDF Require students to click the submit button Yes Attempts reopened Manually Maximum attempts Unlimited On another browser (e.g. incognito window), login as student and upload pdf file to assignment. Save the changes, but do not press " Submit assignment " to leave its status as " Draft ". Back on the teacher's window, go to grading page and grade the student's submission. Make sure PDF feedback is successfully generated. Press " Save changes ". Back on the student's window, upload another file to assignment in docx format. Save the changes but don't submit it. Back on the teacher's window, refresh the grading page. Make sure PDF feedback is successfully generated. Press " Save changes ". Back on the student's browser and delete the docx file from assignment submission.  Save the changes don't submit it. Back on the teacher's window, refresh the grading page. Confirm that the PDF feedback is successfully generated and that the page is not stuck trying to generate the PDF.