                              self.stderr.write("Error: That %s is already taken." % verbose_field_name)
                              username = None
  
                  for field_name in self.UserModel.REQUIRED_FIELDS:
                      field = self.UserModel._meta.get_field(field_name)
                      user_data[field_name] = options[field_name]
                      while user_data[field_name] is None:
 
</s> remove                 verbose_field_name = self.username_field.verbose_name
 </s> add 
                if not username:
                    raise CommandError('%s cannot be blank.' % capfirst(verbose_field_name))

                              self.stderr.write("Error: That %s is already taken." % verbose_field_name)
                              username = None
  
                if not username:
                    raise CommandError('%s cannot be blank.' % capfirst(verbose_field_name))

                  for field_name in self.UserModel.REQUIRED_FIELDS:
                      field = self.UserModel._meta.get_field(field_name)
                      user_data[field_name] = options[field_name]
                      while user_data[field_name] is None:
keep keep add keep keep keep keep
 Fixed #28591 -- Added an error message for createsuperuser --username= (blank). 
django/contrib/auth/management/commands/createsuperuser.py