Cron Error

As follows:

Notice: Trying to get property of non-object in mailchimp_lists_load_user_mergevars() (line 593 of //sites/all/modules/mailchimp/modules/mailchimp_lists/mailchimp_lists.module).

Occurs when running cron

Settings ON:
Sync list during cron
Enable Mailchimp webhooks
Drupal 7.12