## Don't display a preference for an hidden page or space.
        ## Why? If a user has the autowatch option enabled and create a new hidden document (for example, when she creates an application with AWM, hidden code pages are created as well),
        ## we don't want to pollute the livetable with these hidden pages that the user don't know about. Moreover, the notifications will filter events concerning hidden pages,
        ## so even if the filter exists, it has no effect to the user.
        ## Here we handle only the case where pages.size() == 1 or spaces.size() == 1.
        ## In the case there are several elements in the lists, they might have different "hidden" properties, and we don't handle it
        ## Note: in the current implementation of watched entities, it's never the case.
        ## TODO: handle these cases too in case custom filters need this.