see here:  https://www.odoo.com/forum/help-1/question/how-to-display-group-column-with-no-data-in-openerp-7s-kanban-view-30469

By the way solution is 

def _read_group_drivers(self, cr, uid, ids, domain, read_group_order=None, access_rights_uid=None, context=None):
    #search and pass one2many fieldsid and name in list for ex = [(id1,'name'),(id2, 'name2')] and fold 
        all_drivers = self.pool.get('soohoo.driver').search(cr, uid, [])
        #for driver in all_drivers:
        _logger.warning('drivers--------- %s ' %all_drivers)
        result = [(driver.id, driver.name) for driver in self.pool.get('soohoo.driver').browse(cr, uid, all_drivers)]
        fold = dict.fromkeys(range(1,len(result)+1), False)
        _logger.warning('here---- %s ----and----  %s' %(result, fold))
        return result, fold

    _group_by_full = {
        'driver': _read_group_drivers
    }