message: fix the update throw when empty date
diff: @@ -19,7 +19,7 @@ export default function UPDATE(option: {
  protocol: u.protocol,
  host: u.host,
  path: u.path,
  - headers: option.fallback ? { 'If-Modified-Since': option.fallback.date } : undefined
  + headers: option.fallback && option.fallback.date ? { 'If-Modified-Since': option.fallback.date } : undefined
  }, (res: any) => {
  if (res.statusCode == 200) {
  res.setEncoding('utf-8')
  