code: protected Class<?> loadClass(ClassLoader classLoader, String name) {
      // A null classloader is the system classloader.
      classLoader = (classLoader != null) ? classLoader : ClassLoader.getSystemClassLoader();
      return caches.get(classLoader).get(name);
    }
docs: Loads a class from a {@code ClassLoader}-specific cache if it's already there, or
  loads it from the given {@code ClassLoader} and caching it for future requests.  Failures
  to load are also cached using the Void.class type.  A null {@code ClassLoader} is assumed
  to be the system classloader.