code: func (o *Owner) BlobRef() blob.Ref {
  	if o == nil || len(o.blobByKeyID) == 0 {
  		return blob.Ref{}
  	}
  	refs := o.blobByKeyID[o.KeyID()]
  	if len(refs) == 0 {
  		return blob.Ref{}
  	}
  	ref, ok := blob.Parse(refs[0])
  	if !ok {
  		return blob.Ref{}
  	}
  	return ref
  }
docs: // BlobRef returns the currently recommended ref implementation of the owner GPG
  // key blob. Its signature might change when support for multiple hashes and/or
  // multiple GPG keys is introduced.