docs: public static URL classFileUrl(Class<?> clazz) throws IOException {
          ClassLoader cl = clazz.getClassLoader();
          if (cl == null) {
              cl = ClassLoader.getSystemClassLoader();
          }
          URL res = cl.getResource(clazz.getName().replace('.', '/') + ".class");
          if (res == null) {
              throw new IllegalArgumentException("Unable to locate class file for " + clazz);
          }
          return res;
      }