Single view selecting "Choose..." causes errors to appear and bad page to load

There are two ways to reproduce this, one with JS off and one with use of back button: Setup: Create a course wth multiple students enrolled As teacher, Navigate to Course > Grade administration > Single view Non-JS replication: Disable JS On the dropdowns 'Select grade item' select no option and press 'Go' VERIFY: that php errors are not experienced and you just get the same page On the dropdowns 'Select user' select no option and press 'Go' VERIFY: that php errors are not experienced and you just get the same page JS replication: On the 'Select grade item' select, choose a grade item You should be redicted to that grade item's singleview Press your browser back button On the dropdown select the 'Select grade item' (i.e. don't choose a grade item) VERIFY: you do not get a php error. On the 'Select user' select, choose a user You should be redicted to that users singleview Press your browser back button On the dropdown select the 'Select user' option (i.e. don't choose a user) VERIFY: you do not get a php error.