'The nearest zone for this document, starting from this document and
moving upwards via "parent_topic". For a non-default-language document
that does not have its own nearest zone, returns the nearest zone of
its parent (the document it was translated from).'

@cached_property
def nearest_zone(self):

    job = DocumentNearestZoneJob()
    result = job.get(self.pk)
    if ((not result) and self.parent and (self.locale != settings.WIKI_DEFAULT_LANGUAGE)):
        return job.get(self.parent.pk)
    return result
