no in packlist : 
  var json;
  try {
    json = JSON.parse(contents);
  } catch (e) {
    print(e);
    print('Could not parse existing asset pack file: ${out.path}');
    print('Creating new assset pack.');
    // Return empty asset pack file.
    return new AssetPackFile();
  }
  print('Loaded existing asset pack file: ${out.path}');
  return new AssetPackFile.fromJson(json);