code: function parseCustomValue(value, parse) {
    try {
      let parsed = parse(value)
      if (parsed === undefined) {
        return { value: null }
      }
      return { value: parsed }
    } catch (error) {
      return { error: error.message }
    }
  }
docs: Converts textual value to a custom value using supplied `.parse()`.
  @param  {string} value
  @param  {function} parse
  @return {{ value: any, error: string }}