anchor.diff:  
     final bool publish = parsedArguments['publish'] as bool;
     final bool dryRun = parsedArguments['dry_run'] as bool;
  -  final Branch branch = Branch.fromName(parsedArguments['branch'] as String);
  +  final Branch branch = Branch.values.byName(parsedArguments['branch'] as String);
     final ArchiveCreator creator = ArchiveCreator(
       tempDir,
       outputDir,
  
positive.code:     errorExit('Invalid argument: --branch must be specified.');
    }
  
    final String tempDirArg = parsedArguments['temp_dir'] as String;
    Directory tempDir;
    bool removeTempDir = false;
    if (tempDirArg == null || tempDirArg.isEmpty) {
  
negative.code:     exit(exitCode);
    }
  
    if (!parsedArguments.wasParsed('revision')) {
      errorExit('Invalid argument: --revision must be specified.');
    }
    final String revision = parsedArguments['revision'] as String;
    if (revision.length != 40) {
      errorExit('Invalid argument: --revision must be the entire hash, not just a prefix.');
    }
  