code: public static Set<Asset> resolveAssets(MinecraftDirectory minecraftDir, String assets) throws IOException {
  		Objects.requireNonNull(minecraftDir);
  		Objects.requireNonNull(assets);
  		if (!minecraftDir.getAssetIndex(assets).isFile()) {
  			return null;
  		}
  
  		try {
  			return getVersionParser().parseAssetIndex(IOUtils.toJson(minecraftDir.getAssetIndex(assets)));
  		} catch (JSONException e) {
  			throw new IOException("Couldn't parse asset index: " + assets, e);
  		}
  	}
docs: Resolves the asset index.
  
  @param minecraftDir the minecraft directory
  @param assets the name of the asset index, you can get this via
  {@link Version#getAssets()}
  @return the asset index, null if the asset index does not exist
  @throws IOException if an I/O error has occurred during resolving asset
  index
  @throws NullPointerException if
  <code>minecraftDir==null || assets==null</code>