docs: def combine_locks(locks):
      """Combine a sequence of locks into a single lock."""
      all_locks = []
      for lock in locks:
          if isinstance(lock, CombinedLock):
              all_locks.extend(lock.locks)
          elif lock is not None:
              all_locks.append(lock)
  
      num_locks = len(all_locks)
      if num_locks > 1:
          return CombinedLock(all_locks)
      elif num_locks == 1:
          return all_locks[0]
      else:
          return DummyLock()