func (tg *Group) UnmarshalJSON(b []byte) error {
	g := struct {
		Targets []string       `json:"targets"`
		Labels  model.LabelSet `json:"labels"`
	}{}

	dec := json.NewDecoder(bytes.NewReader(b))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&g); err != nil {
		return err
	}
	tg.Targets = make([]model.LabelSet, 0, len(g.Targets))
	for _, t := range g.Targets {
		tg.Targets = append(tg.Targets, model.LabelSet{
			model.AddressLabel: model.LabelValue(t),
		})
	}
	tg.Labels = g.Labels
	return nil
}
func (tg *Group) UnmarshalJSON(b []byte) error {
	g := struct {
		Targets []string       `json:"targets"`
		Labels  model.LabelSet `json:"labels"`
	}{}

	dec := json.NewDecoder(bytes.NewReader(b))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&g); err != nil {
		return err
	}
	tg.Targets = make([]model.LabelSet, 0, len(g.Targets))
	for _, t := range g.Targets {
		tg.Targets = append(tg.Targets, model.LabelSet{
			model.AddressLabel: model.LabelValue(t),
		})
	}
	tg.Labels = g.Labels
	return nil
}
// UnmarshalJSON implements the json.Unmarshaler interface.