extra character "\" when dart process pass argument end with "\"

[Ticore]

windows 8, dart sdk 1.12.0-dev.1.1

import 'dart:io';
main() async {
  print((await Process.run('cmd', ['/c', r'echo c:\'])).stdout);
  // output with extra character: c:\\
  print((await Process.run('cmd', ['/c', r'echo c:\.'])).stdout);
  // output normal: c:\.
}