docs: public Class<?> getClass(int id) throws IOException {
        if (id < 0 || id > internalIdToClass.length) {
           throw new IOException("Unknown class id " + id);
        }
        Class<?> clazz = internalIdToClass[id];
        if (clazz == null) {
           throw new IOException("Unknown class id " + id);
        }
        return clazz;
     }