'Merge Item objs by copying missing fields from items in the tail to
the head item.
Return same number of items, with the head item modified.'

def _merge_items(self, objs):

    fields = Item.all_keys()
    for f in fields:
        for o in objs[1:]:
            if (getattr(objs[0], f, None) in (None, '')):
                value = getattr(o, f, None)
                if value:
                    self._log.debug(u'key    {0}    on    item    {1}    is    null    or    empty:    setting    from    item    {2}', f, displayable_path(objs[0].path), displayable_path(o.path))
                    setattr(objs[0], f, value)
                    objs[0].store()
                    break
    return objs
