fixes #3156

Closes #3156

Merge request studip/studip!2132

app/controllers/my_courses.php

@@ -401,7 +401,10 @@ class MyCoursesController extends AuthenticatedController
 
         // Ensure last teacher cannot leave course
         $course = Course::find($course_id);
-        if ($course->members->findOneBy('user_id', $GLOBALS['user']->id)->status === 'dozent'
+        $teacher = $course->members->findOneBy('user_id', User::findCurrent()->id);
+        if (
+            $teacher
+            && $teacher->status === 'dozent'
             && count($course->getMembersWithStatus('dozent')) === 1
         ) {
             PageLayout::postError(sprintf(

lib/messaging.inc.php

@@ -161,7 +161,8 @@ class messaging
         $msg      = Message::find($message_id);
         $receiver = User::find($rec_user_id);
         $to       = $receiver->Email;
-
+        $reply_to = '';
+        $snd_fullname = '';
         // do not try to send mails to users without a mail address
         if (!$to) {
             return;