ClassFileTransformer.transform() can be passed null className

Agent.java

import java.lang.instrument.Instrumentation;
 
public class Agent {
    public static void premain(String agentArgs, Instrumentation instrumentation) {
        instrumentation.addTransformer(new Transformer());
    }
}

Main.java

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;

public class Main {

    public static void main(String... args) throws Exception {
        MethodType mt = MethodType.methodType(String.class);
        MethodHandle mh = MethodHandles.lookup().findVirtual(Object.class, "toString", mt);
    }
}

MANIFEST.MF

Premain-Class: Agent

SAMPLE OUTPUT

className is null
className is null
className is null
className is null
className is null
className is null

test.sh

#!/bin/sh

javac Agent.java Transformer.java Main.java
jar cmf MANIFEST.MF agent.jar Agent.class Transformer.class Main.class
java -javaagent:agent.jar Main

Transformer.java

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
 
public class Transformer implements ClassFileTransformer {
    @Override
    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
            ProtectionDomain protectionDomain, byte[] classfileBuffer)
            throws IllegalClassFormatException {
        if (className == null) {
            System.out.println("className is null");
        }
        return null;
    }
}