Resolve error "Creating default object from empty value"

See related support threads:

http://wordpress.org/support/topic/gravity-forms-exacttarget-add-on-conflicting-with-latest-version-1
http://wordpress.org/support/topic/error-message-warning-creating-default-object-from-empty-value

Current version displays following error on ExactTarget settings page and upon any form submission:

```
Warning: Creating default object from empty value in D:\WebSites\berry-r00-dev-web\wp-content\plugins\gravity-forms-exacttarget\api\ExactTarget.class.php on line 43
```

Using current plugin versions as of pull request.

- Gravity Forms 1.8.8.9
- Gravity Forms ExactTarget Add-On 1.0.6