code: func (t taxonomyNodeInfos) GetOrAdd(plural, term string) *taxonomyNodeInfo {
  	parent := t.GetOrCreate(plural, "")
  	if parent == nil {
  		panic(fmt.Sprintf("no parent found with plural %q", plural))
  	}
  	child := t.GetOrCreate(plural, term)
  	child.parent = parent
  	return child
  }
docs: // GetOrAdd will get or create and add a new taxonomy node to the parent identified with plural.
  // It will panic if the parent does not exist.