Undefined index: cc_newsletter in constant_contact_user_update()

We are getting the following message in the log when unblocking new user registrations.

Notice: Undefined index: cc_newsletter in constant_contact_user_update() (line 733 of /sites/all/modules/contrib/constant_contact/constant_contact.module).

The user seems to still get signed up for the newsletter and the account does get activated. I ran several scenarios to reproduce including...

Registering a new user account (admin approval required)
Unblock the account using VBO or by editing the user account
Notice shows in the logs

It looks like if the user is already subscribed the following error is returned as well...

Sorry there was a problem communicating with the constant contact server, the error given was: Invalid Request which has been reported here --> https://www.drupal.org/node/716574