code: func (t Type) Union() ([]string, bool) {
  	if !t.IsUnion() {
  		return nil, false
  	}
  	tips := []string{}
  	for _, ut := range strings.Split(t.TypeString(), "|") {
  		tips = append(tips, strings.TrimSpace(ut))
  	}
  	return tips, true
  }
docs: // Union returns union type of this type