          test(self)
  
      def test_invalid_username(self):
          """Creation fails if the username fails validation."""
          user_field = User._meta.get_field(User.USERNAME_FIELD)
          new_io = StringIO()
          entered_passwords = ['password', 'password']
 
</s> remove                 verbose_field_name = self.username_field.verbose_name
 </s> add 
    def test_blank_username(self):
        """Creation fails if --username is blank."""
        new_io = StringIO()

        def test(self):
            with self.assertRaisesMessage(CommandError, 'Username cannot be blank.'):
                call_command(
                    'createsuperuser',
                    username='',
                    stdin=MockTTY(),
                    stdout=new_io,
                    stderr=new_io,
                )

        test(self)

          test(self)
  
    def test_blank_username(self):
        """Creation fails if --username is blank."""
        new_io = StringIO()

        def test(self):
            with self.assertRaisesMessage(CommandError, 'Username cannot be blank.'):
                call_command(
                    'createsuperuser',
                    username='',
                    stdin=MockTTY(),
                    stdout=new_io,
                    stderr=new_io,
                )

        test(self)

      def test_invalid_username(self):
          """Creation fails if the username fails validation."""
          user_field = User._meta.get_field(User.USERNAME_FIELD)
          new_io = StringIO()
          entered_passwords = ['password', 'password']
keep add keep keep keep keep keep
 Fixed #28591 -- Added an error message for createsuperuser --username= (blank). 
tests/auth_tests/test_management.py