Error in Embargo Workflow Job when document with trigger is deleted

If a document that has an embargo schedule on it (to enforce or lift an embargo on a later moment) is deleted, the Embargo Workflow Job still tries to update the document, which leads to an error:

org.onehippo.forge.embargo.repository.workflow.EmbargoWorkflowImpl$WorkflowJob Execution of scheduled workflow operation
[removeEmbargo, null] on javax.jcr.ItemNotFoundException: 049e16ed-d4b0-44c0-98a5-4a81e7020bf1failed

The node for the deleted document in /content/attic includes the embargo trigger. By deleting this node manually form console the errors will be stopped. 

Reproducing of the bug

• Make a document under embargo
• Schedule it to be removed after 5 minutes
• Delete the document and check the log
• Check the document that is in attic and includes hipposched:triggers node

The best solution would be to prevent deletion if an embargo schedule is still valid for the node. That would match with the regular publish/depublish triggers for documents. But that will require changes in the CMS or customizations to it when the embargo plugin is present. That will be in intrusive change.

Proposed solution: update the Embargo Workflow Job so it ignores nodes under /content/attic.