Forward port CMS7-6949: DocumentService returns null, and doesn't invoke the rest service

Forward port of CMS7-6949 into Channel Manager trunk and 2.24.xx branch.
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When a document which isn't rendered through a channel get's published the document service should return an empty list which is used to render the ChannelWorkflowActions menu. The invoked service DocumentsResource does return in any case an empty list but not null. When setting a beakpoint on getChannels of DocumentsResource, the method seems not to get called. Using the latest apache-xcf framework release 2.6.6 of the 2.6.x branch, does provide same results.