Created attachment 1071860 [details]
Output of foreman-debug from a RHEL 7.1 system.

Document URL: 
https://satellite6.example.com/apidoc/v2/content_view_versions/incremental_update.html

Section Number and Name: 

Describe the issue:
The API docs mark each portion of an API call as either "required" or "optional". The update_systems[included] portion of the `POST /katello/api/content_view_versions/incremental_update` call is marked as required. But this is not true. It's definitely possible to perform an incremental update without specifying this bit of information.

Suggestions for improvement: 

Additional information: 
A test for this issue is in place. This [1] pull request performs an incremental update and passes the following JSON payload:

    payload = {
        'content_view_version_environments': [{
            'content_view_version_id': content_view.version[0].id,
            'environment_ids': [
                environment.id
                for environment
                in content_view.version[0].read().environment
            ],
        }],
        'add_content': {'puppet_module_ids': [puppet_module.id]},
    }

[1] https://github.com/SatelliteQE/robottelo/pull/2739