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/test/java/org/elasticsearch/test/SecurityIntegTestCase.java
assertSecurityIndexActive(cluster());
    }
    public void assertSecurityIndexActive(TestCluster testCluster) throws Exception {
        for (Client client : testCluster.getClients()) {
            assertBusy(() -> {
                ClusterState clusterState = client.admin().cluster().prepareState().setLocal(true).get().getState();
                assertFalse(clusterState.blocks().hasGlobalBlock(GatewayService.STATE_NOT_RECOVERED_BLOCK));
                Index securityIndex = resolveSecurityIndex(clusterState.metadata());
                if (securityIndex != null) {
                    IndexRoutingTable indexRoutingTable = clusterState.routingTable().index(securityIndex);
                    if (indexRoutingTable != null) {
                        assertTrue(indexRoutingTable.allPrimaryShardsActive());
                    }
                }
            }, 30L, TimeUnit.SECONDS);
        }
    }
    protected void deleteSecurityIndex() {
        final Client client = client().filterWithHeader(
            Collections.singletonMap(
                "Authorization",
                UsernamePasswordToken.basicAuthHeaderValue(
                    SecuritySettingsSource.ES_TEST_ROOT_USER,
                    SecuritySettingsSourceField.TEST_PASSWORD_SECURE_STRING
                )
            )
        );
        GetIndexRequest getIndexRequest = new GetIndexRequest();
        getIndexRequest.indices(SECURITY_MAIN_ALIAS);
        getIndexRequest.indicesOptions(IndicesOptions.lenientExpandOpen());