code: func timeDurationToStringHookFunc() mapstructure.DecodeHookFunc {
  	return func(
  		f reflect.Type,
  		t reflect.Type,
  		data interface{}) (interface{}, error) {
  		dur, ok := data.(time.Duration)
  		if !ok {
  			return data, nil
  		}
  		if t.Kind() != reflect.String {
  			return data, nil
  		}
  		if dur == 0 {
  			return "", nil
  		}
  
  		// Convert it by parsing
  		return data.(time.Duration).String(), nil
  	}
  }
docs: // timeDurationToStringHookFunc returns a DecodeHookFunc that converts
  // time.Duration to string.