code: func (w *writer) writeOneValReflect(id quad.Value, pred quad.Value, rv reflect.Value, rev bool) error {
  	if isZero(rv) {
  		return nil
  	}
  	// write field value and get an ID
  	sid, err := w.writeAsQuads(rv)
  	if err != nil {
  		return err
  	}
  	// write a quad pointing to this value
  	return w.writeQuad(id, pred, sid, rev)
  }
docs: // writeOneValReflect writes a set of quads corresponding to a value. It may omit writing quads if value is zero.