Error When Submitting Webform With Single Default Value and Merge Vars

We were getting an error when submitting with our webform following along with the tutorial here: https://interactiveknowledge.com/insights/how-use-drupal-constant-contac...

The error involved the single default value that we had set on the webform and a PHP error saying that the submitted value wasn't "countable". It seemed to be expecting an array and we're only allowing our customers to sign up for a single list with this form. I've also written a patch to fix this and will be attaching that in a follow-up comment.