code: func (g *rfc4122Generator) NewV4() (UUID, error) {
  	u := UUID{}
  	if _, err := io.ReadFull(g.rand, u[:]); err != nil {
  		return Nil, err
  	}
  	u.SetVersion(V4)
  	u.SetVariant(VariantRFC4122)
  
  	return u, nil
  }
docs: // NewV4 returns random generated UUID.