code: public static Optional<MediaType> byExtension(final String ext) {
      requireNonNull(ext, "An ext is required.");
      String key = "mime." + ext;
      if (types.hasPath(key)) {
        return Optional.of(MediaType.valueOf(types.getString("mime." + ext)));
      }
      return Optional.empty();
    }
docs: Get a {@link MediaType} for a file extension.
  
  @param ext A file extension, like <code>js</code> or <code>css</code>.
  @return A {@link MediaType} or empty optional for unknown file extensions.