plugin/param.go
func (p ParamSet) Unmarshal(v interface{}) error {
	return json.NewDecoder(p.reader).Decode(v)
}
func (p ParamSet) Unmarshal(v interface{}) error {
	return json.NewDecoder(p.reader).Decode(v)
}
// Unmarshal parses the JSON payload from the command
// arguments and unmarshal into a value pointed to by v.