NPE in ServiceCacheImpl.start() because child.getData() returns null

This problem is in curator-discovery module where we get an NPE on ServiceProvider.start() because child.getData() can be null while starting ServiceCacheImpl. This is similar to https://issues.apache.org/jira/browse/CURATOR-452 but happens on adding null to map.

NPE Stacktrace

java.lang.NullPointerException at java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011) ~[?:1.8.0_112] at java.util.concurrent.ConcurrentHashMap.putIfAbsent(ConcurrentHashMap.java:1535) ~[?:1.8.0_112] at org.apache.curator.x.discovery.details.ServiceCacheImpl.addInstance(ServiceCacheImpl.java:196) ~[curator-x-discovery-4.0.0.jar:?] at org.apache.curator.x.discovery.details.ServiceCacheImpl.start(ServiceCacheImpl.java:96) ~[curator-x-discovery-4.0.0.jar:?] at org.apache.curator.x.discovery.details.ServiceProviderImpl.start(ServiceProviderImpl.java:75) ~[curator-x-discovery-4.0.0.jar:?]

The code

client = CuratorFrameworkFactory.newClient("localhost:2181", new ExponentialBackoffRetry(1000, 3));

client.start();

serviceDiscovery = ServiceDiscoveryBuilder.builder(ServiceRecord.class).client(client).basePath("/discovery/services/").serializer(serializer).build(); serviceDiscovery.start();

serviceProvider = serviceDiscovery.serviceProviderBuilder().serviceName(serviceName).build();

serviceProvider.start();