Jekyll server creates empty folder in root, differs from destination:

My source directory is ~/Sites/rtt-jekyll

My build settings in _config.yml include the following option and value:
destination: ~/Sites/rtt-deploy

When I run bundle exec jekyll build everything works as expected, and the built site appears in ~/Sites/rtt-deploy as expected

when I run bundle exec jekyll serve, the site is built in, and is served from, the correct path, but the serve command also creates a new, empty directory within the source directory:

I’ve tried to puzzle out what this might be caused by but haven’t been able to figure it out. It’s not a big deal, but the creation of the empty directory adds clutter and could be confusing.

Source can be found:

Grateful for your insights!

Delete the empty deploy directory and let me know if the following works…?

destination: "../rtt-deploy"