Merge branch 'master' of https://github.com/TEAMMATES/repo
Merge branch 'master' of https://github.com/TEAMMATES/repo
Added test cases to cover the new conditions added
Merge branch 'master' of https://github.com/TEAMMATES/repo into Issue1871
restored null checks in the action page
minor indentation issue
[1871] Clean up InstructorFeedbackPreviewAsStudentAction

fixes #1871