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
fake,
            "description",
            "description",
            "name",
            "fake",
            "version",
            "1.0.0",
            "elasticsearch.version",
            Version.CURRENT.toString(),
            "java.version",
            System.getProperty("java.specification.version"),
            "classname",
            "test.DummyPlugin"
        );
        try (InputStream jar = PluginsServiceTests.class.getResourceAsStream("dummy-plugin.jar")) {
            Files.copy(jar, fake.resolve("plugin.jar"));
        }
        final Settings settings = Settings.builder().put("path.home", pathHome).put("plugin.mandatory", "fake").build();
        var pluginsService = newPluginsService(settings);
        closePluginLoaders(pluginsService);
    }
    public void testPluginFromParentClassLoader() throws IOException {
        final Path pathHome = createTempDir();
        final Path plugins = pathHome.resolve("plugins");
        final Path fake = plugins.resolve("fake");
        PluginTestUtil.writePluginProperties(
            fake,
            "description",
            "description",
            "name",