code: func (k cursorKind) fetchPrevCursor(c context.Context, pkg, cursor string) string {
  	itm, err := memcache.GetKey(c, k.cursorKey(pkg, cursor))
  	if err != nil {
  		if err != memcache.ErrCacheMiss {
  			logging.WithError(err).Errorf(c, "Failed to fetch prev cursor %q from memcache", k)
  		}
  		return ""
  	}
  	return string(itm.Value())
  }
docs: // fetchPrevCursor returns a cursor stored by storePrevCursor.
  //
  // Logs and ignores errors. Cursor mapping is non-essential functionality.