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.
x-pack/plugin/security/src/internalClusterTest/java/org/elasticsearch/test/SecuritySingleNodeTestCase.java
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.transport.TransportAddress;
import org.elasticsearch.core.IOUtils;
import org.elasticsearch.http.HttpInfo;
import org.elasticsearch.license.LicenseSettings;
import org.elasticsearch.plugins.Plugin;
import org.elasticsearch.xpack.core.security.authc.support.Hasher;
import org.elasticsearch.xpack.security.LocalStateSecurity;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Rule;
import org.junit.rules.ExternalResource;
import java.net.InetSocketAddress;
import java.nio.file.Path;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import java.util.stream.Collectors;
import static org.elasticsearch.test.SecuritySettingsSourceField.TEST_PASSWORD_SECURE_STRING;
import static org.elasticsearch.xpack.core.security.authc.support.UsernamePasswordToken.basicAuthHeaderValue;
import static org.hamcrest.Matchers.hasItem;
/**
 * A test that starts a single node with security enabled. This test case allows for customization
 * of users and roles that the cluster starts with. If an integration test is needed to test but
 * multiple nodes are not needed, then this class should be favored over
 * {@link SecurityIntegTestCase} due to simplicity and improved speed from not needing to start
 * multiple nodes and wait for the cluster to form.
 */
public abstract class SecuritySingleNodeTestCase extends ESSingleNodeTestCase {