ByteBuddy fails when trying to redefine sun.reflect.GeneratedMethodAccessor1

Driven by curiosity, I tried to export the bytecode of GeneratedMethodAccessor1 (generated by the JVM when using reflection).

I try to get the bytecode of the class the following way:

public class MethodExtractor {

    public int extract() {
        return new Random().nextInt();
    }

    public static void main(String[] args) throws Exception {

        ExampleClass example = new ExampleClass();

        Method exampleMethod = ExampleClass.class
                .getDeclaredMethod("exampleMethod");
        exampleMethod.setAccessible(true);

        int rndSum = 0;
        for (int i = 0; i < 20; i++) {
            rndSum += (Integer) exampleMethod.invoke(example);
        }

        Field field = Method.class.getDeclaredField("methodAccessor");
        field.setAccessible(true);
        Object methodAccessor = field.get(exampleMethod);
        Field delegate = methodAccessor.getClass().getDeclaredField("delegate");
        delegate.setAccessible(true);
        Object gma = delegate.get(methodAccessor);

        ByteBuddyAgent.installOnOpenJDK();
        try {
            ClassFileLocator classFileLocator = ClassFileLocator.AgentBased
                    .fromInstalledAgent(gma.getClass().getClassLoader());
            Unloaded<? extends Object> unloaded = new ByteBuddy().redefine(
                    gma.getClass(), classFileLocator).make();
            Map<TypeDescription, File> saved = unloaded.saveIn(Files
                    .createTempDirectory("javaproxy").toFile());
            saved.forEach((t, u) -> System.out.println(u.getAbsolutePath()));
        } catch (IOException e) {
            throw new RuntimeException("Failed to save class to file");
        }
    }
}

I however get the following error when executing this class:

Exception in thread "main" java.lang.NullPointerException
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Engine$ForRedefinition.create(TypeWriter.java:172)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:1182)
    at net.bytebuddy.dynamic.scaffold.inline.InlineDynamicTypeBuilder.make(InlineDynamicTypeBuilder.java:244)
    at reegnz.dyna.proxy.extractor.MethodExtractor.main(MethodExtractor.java:48)

Basically I first iterate on the method call enough times for the JVM to inflate the method (generate the GeneratedMethodAccessor) and then try to redefine the class to get the bytecode.

I tried the same method to export a generated Proxy class, and it worked flawlessly. That's what drove me to try this.

It seems that the DelegatingClassLoader of the GeneratedMethodAccessor1 class can't even reload the class when I try to load the class with the loadClass method.

Any ideas how I could retrieve the bytecode for GeneratedMethodAccessor classes?