docs: def get(ns, dburl=None):
      '''
      Get a default dones object for ns.  If no dones object exists for ns yet,
      a DbDones object will be created, cached, and returned.
      '''
      if dburl is None:
          dburl = DONES_DB_URL
  
      cache_key = (ns, dburl)
      if ns not in DONES_CACHE:
          dones_ns = 'dones_{}'.format(ns)
          DONES_CACHE[cache_key] = DbDones(ns=dones_ns, dburl=dburl)
  
      return DONES_CACHE[cache_key]