code: @Implementation
    protected AssetFileDescriptor openRawResourceFd(int id) throws Resources.NotFoundException {
      if (isLegacyAssetManager()) {
        InputStream inputStream = openRawResource(id);
        if (!(inputStream instanceof FileInputStream)) {
          // todo fixme
          return null;
        }
  
        FileInputStream fis = (FileInputStream) inputStream;
        try {
          return new AssetFileDescriptor(ParcelFileDescriptor.dup(fis.getFD()), 0,
              fis.getChannel().size());
        } catch (IOException e) {
          throw newNotFoundException(id);
        }
      } else {
        return directlyOn(realResources, Resources.class).openRawResourceFd(id);
      }
    }
docs: Since {@link AssetFileDescriptor}s are not yet supported by Robolectric, {@code null} will be
  returned if the resource is found. If the resource cannot be found, {@link
  Resources.NotFoundException} will be thrown.