code: func filterExisting(c context.Context, fwdDeps []*model.FwdDep) ([]*model.FwdDep, error) {
  	ret := make([]*model.FwdDep, 0, len(fwdDeps))
  
  	err := ds.Get(c, fwdDeps)
  	if err == nil {
  		return nil, nil
  	}
  
  	merr, ok := err.(errors.MultiError)
  	if !ok {
  		return nil, err
  	}
  
  	for i, err := range merr {
  		if err == nil {
  			continue
  		}
  		ret = append(ret, fwdDeps[i])
  	}
  
  	return ret, nil
  }
docs: // filterExisting removes the FwdDep objects which already exist.
  //
  // returns gRPC code error.