Issue with token (advanced) mode in field instance

Notice: Undefined index: merge_vars in _mailchimp_lists_field_instance_settings_form_process() (line 226 of /var/www/mysite.com/sites/all/modules/contrib/mailchimp/modules/mailchimp_lists/includes/mailchimp_lists.field.inc).
Warning: Invalid argument supplied for foreach() in _mailchimp_lists_field_instance_settings_form_process() (line 226 of /var/www/mysite.com/sites/all/modules/contrib/mailchimp/modules/mailchimp_lists/includes/mailchimp_lists.field.inc).

Looking at the .field.inc file, and inspecting this section, starting with line 226:

    foreach ($mergevars[$mc_list_id]['merge_vars'] as $mergevar) {
      $form[$mergevar->tag] += array(
        '#element_validate' => array('token_element_validate'),
        '#token_types' => array($instance['entity_type']),
      );

it seems that this should actually read

    foreach ($mergevars[$mc_list_id] as $mergevar) {
      $form[$mergevar->tag] += array(
        '#element_validate' => array('token_element_validate'),
        '#token_types' => array($instance['entity_type']),
      );

as the array $mergevars[$mc_list_id] doesn't have a 'merge_vars' key, but is a simple array of settings for each merge field.