code: func (j *Json) CheckGet(key string) (*Json, bool) {
  	m, err := j.Map()
  	if err == nil {
  		if val, ok := m[key]; ok {
  			return &Json{val}, true
  		}
  	}
  	return nil, false
  }
docs: // CheckGet returns a pointer to a new `Json` object and
  // a `bool` identifying success or failure
  //
  // useful for chained operations when success is important:
  //    if data, ok := js.Get("top_level").CheckGet("inner"); ok {
  //        log.Println(data)
  //    }