code: func (o *Owner) RefSet(keyID string) SignerRefSet {
  	if o == nil || len(o.blobByKeyID) == 0 {
  		return nil
  	}
  	refs := o.blobByKeyID[keyID]
  	if len(refs) == 0 {
  		return nil
  	}
  	return refs
  }
docs: // RefSet returns the set of refs that represent the same owner as keyID.