Company duplicates

Question

I use gtags, jedi and dabbrev for python. Sometimes the duplicates get a bit annoying. I read that using :with should sort out the duplicates problem. However, it does not... Is there a better solution that this? :

(add-hook 'python-mode-hook
          (lambda ()
            (set (make-local-variable 'company-backends)
                 '((company-gtags :with company-jedi company-dabbrev-code)))))

In the Company documentation, Company Backends section there is a line that reads: "‘duplicates’: If non-nil, company will take care of removing duplicates from the list.". I just can't figure out how to enable it.