code: private static Constructor<?> createImpl(Class<?> cl,
                                             ClassLoader loader)
    {
      /**
      if (! Modifier.isAbstract(cl.getModifiers())) {
        throw new IllegalArgumentException();
      }
      */
      
      ClassGeneratorVault<?> generator
        = new ClassGeneratorVault<>(cl, loader);
      
      Class<?> proxyClass = generator.generate();
      
      return proxyClass.getConstructors()[0];
    }
docs: Must return Constructor, not MethodHandle because MethodHandles
  cache the type in the permgen.