anchor.diff:          abbr: 'h', help: 'Print this usage information.', negatable: false)
       ..addFlag('version',
           help: 'Print the version of Dart Sass.', negatable: false);
  -  var options = argParser.parse(args);
  +
  +  ArgResults options;
  +  try {
  +    options = argParser.parse(args);
  +  } on FormatException catch (error) {
  +    _printUsage(argParser, error.message);
  +    exitCode = 64;
  +    return;
  +  }
   
     if (options['version'] as bool) {
       _loadVersion().then((version) {
  
positive.code:       .split(" ")
        .last;
  }
  
negative.code:   }
  
    if (options['help'] as bool || options.rest.isEmpty) {
      _printUsage(argParser, "Compile Sass to CSS.");
      exitCode = 64;
      return;
    }
  