code: func (v *FloatString) MarshalJSON() ([]byte, error) {
  	if v.Valid {
  		strVal := strconv.FormatFloat(v.Value, 'g', -1, 64)
  		return []byte(strVal), nil
  	}
  
  	return []byte(`"null"`), nil
  }
docs: // MarshalJSON implements custom marshalling for FloatString type