Fix in message teacher name

courses/models.py

@@ -766,7 +766,7 @@ class ProfessorMessage(models.Model):
     )
 
     def __str__(self):
-        return self.professor.name + " - " + self.subject + " - " + str(self.date)
+        return self.subject + " - " + str(self.date)
 
     def send(self):
         # bcc = list with all destinataries