Messages external functions fail when trying to retrieve information for deleted or the noreply user

As admin or teacher, create a course with an assignment with online text submissions enabled As student, in your messaging options enable "Popup notifications" for the assignment module. As the same student, submit some text in the assignment As admin, enable "Mobile services": Plugins ► Web Services ► Mobile Create a Token for the student user: Click on Site administration ► Plugins ► Web services ► Manage tokens Next, you can do a CURL REST call simulating a WS client. You need to replace the wstoken and URL. curl 'http://localhost/m/stable_master/webservice/rest/server.php?moodlewsrestformat=json' --data 'wsfunction=core_message_get_contacts&wstoken=ffbe3a3002f235bf9d01fd9369e10b66&moodlewssettingfilter=true' Note, you can use jsonlint.com to validate and format the json returned string or append "| python -m json.tool" to automatically format the command output Confirm that The json returned displays the noreplyuser (-10) in the strangers array