Description of problem: Doing a : hammer capsule synchronize will happily sync your capsule even if nothing is attached to sync. It should throw an error if there is nothing to sync explaining that lifecycle environments need to be attached.
Created redmine issue http://projects.theforeman.org/issues/6673 from this bug
Proposed fix in Katello PR: https://github.com/Katello/katello/pull/4489
Based on feedback on the PR in comment #3, we did not merge the proposed changes. It appears that there is a valid use case for performing a sync on a capsule that has no lifecycle environments attached. For example, it would help to clear a capsule if for some reason the server didn't automatically initiate the cleanup when the lifecycle environments are removed. For this BZ, it might be useful to return a 'warning' to the user; however, given that we do not do anything like that today for other APIs, we are going to move this bug to a future release.
I am closing this based on usptream discussions at https://github.com/Katello/katello/pull/4489. If you disagree, please reopen with your reasoning.