Unknown engine type version-control

Under drush 7.x-4.5, the following command worked well for backing up the site database:

drush @site sql-dump --result-file --gzip

where @site was defined in .drush/aliases.drushrc.php as:

$aliases['site'] = array(
    'uri' => 'example.com',
    'root' => '/var/www/html/drupal',
  );

After replacing drush 7.x-4.5 with drush 7.x-5.0, an error occurred after running the above command:

[user@example.com ~]$ drush @site sql-dump --result-file --gzip
Unknown engine type version-control                                  [error]
No path was set for including the version-control engine backup.     [error]
PHP Fatal error:  Call to a member function prepare_backup_dir() on a non-object in /home/example.com/drush/commands/sql/sql.drush.inc on line 345
Drush command terminated abnormally due to an unrecoverable error.   [error]
Error: Call to a member function prepare_backup_dir() on a non-object
in /home/example.com/drush/commands/sql/sql.drush.inc, line 345

Any ideas?