docs: public static URL getResource(String resourceName) {
          final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
          final ClassLoader loader = contextClassLoader == null ? Resources.class.getClassLoader() : contextClassLoader;
          final URL url = loader.getResource(resourceName);
          if (url == null) {
              throw new IllegalArgumentException("resource " + resourceName + " not found.");
          }
          return url;
      }