We pass `null` for the class name here:

https://github.com/elastic/elasticsearch/blob/f086dd18ddc705bf84a1ff99d35196ec2498fd52/server/src/main/java/org/elasticsearch/plugins/PluginDescriptor.java#L261

However the class name is mandatory for the transport protocol today:

https://github.com/elastic/elasticsearch/blob/f086dd18ddc705bf84a1ff99d35196ec2498fd52/server/src/main/java/org/elasticsearch/plugins/PluginDescriptor.java#L156

This prevents various APIs from working in a cluster with stable plugins installed.
server/src/test/java/org/elasticsearch/plugins/PluginsServiceTests.java
});
        assertThat(
            e,
            hasToString(
                containsString(
                    "no unique public constructor for extension ["
                        + TestExtension.class.getName()
                        + "] of type ["
                        + TestExtensionPoint.class.getName()
                        + "]"
                )
            )
        );
    }
    public void testBadSingleParameterConstructor() {
        TestPlugin plugin = new TestPlugin();
        IllegalStateException e = expectThrows(IllegalStateException.class, () -> {
            PluginsService.createExtension(BadSingleParameterConstructorExtension.class, TestExtensionPoint.class, plugin);
        });
        assertThat(
            e,
            hasToString(
                containsString(
                    "signature of constructor for extension ["
                        + BadSingleParameterConstructorExtension.class.getName()
                        + "] of type ["
                        + TestExtensionPoint.class.getName()
                        + "] must be either () or ("
                        + TestPlugin.class.getName()
                        + "), not ("