Looking through JbpmWorkflowManager shows some deprecated concepts. We need to re-iterate over:
info.magnolia.module.workflow.jbpm.JbpmWorkflowManager#completeWorkItem

• checking for present parameters is obsolete and refers to publication related work items. The method is further more not used for actually completing a work item in the human task context. Still it is valid in the context of completing service tasks of an kind
• info.magnolia.module.workflow.jbpm.JbpmWorkflowManager#getWorkItem
  This one should not be used anymore. it was used to finish a work item for human tasks. Further more the wrapper we initialize only hold the mgnlData map.
• the hardcoded mgnlData parameter should at least be configurable. Further more it might be of value to not put a map inside a map.