druid 0.11.0 kafka-emitter extension exception

[zhou...@gmail.com]

## I already uploaded kafka-emitter jars to the extensions directory and loaded the extension.

```

[root@gpsegment1 druid-0.11.0]# ls extensions/kafka-emitter/

kafka-clients-0.10.2.0.jar  kafka-emitter-0.11.0.jar  lz4-1.3.0.jar  slf4j-api-1.6.4.jar  snappy-java-1.1.2.6.jar

[root@gpsegment1 druid-0.11.0]# grep "kafka-emitter" /opt/druid-0.11.0/conf/druid/_common/common.runtime.properties 

druid.extensions.loadList=["druid-hdfs-storage", "kafka-emitter", "druid-caffeine-cache", "druid-kafka-indexing-service", "mysql-metadata-storage", "druid-datasketches", "druid-histogram"]

[root@gpsegment1 druid-0.11.0]# grep "emitter.kafka" /opt/druid-0.11.0/conf/druid/_common/common.runtime.properties 

druid.emitter=kafka

druid.emitter.logging.logLevel=info

druid.emitter.kafka.bootstrap.servers=192.168.1.115:9092

druid.emitter.kafka.metric.topic=druid-metrics-monitor

druid.emitter.kafka.alert.topic=druid-metrics-alert

druid.emitter.kafka.producer.config={"max.block.ms":10000}

```

## When i start the service ,error occur.but under version 0.10.0, kafka-emitter works normally.my kafka version is 0.10.2. Is this a bug?

2017-12-27T15:55:43,216 INFO [main] io.druid.guice.JsonConfigurator - Loaded class[class io.druid.curator.ExhibitorConfig] from props[druid.exhibitor.service.] as [io.druid.curator.ExhibitorConfig@20a7953c]

2017-12-27T15:55:43,337 INFO [main] org.apache.curator.utils.Compatibility - Running in ZooKeeper 3.4.x compatibility mode

2017-12-27T15:55:43,340 WARN [main] org.apache.curator.retry.ExponentialBackoffRetry - maxRetries too large (30). Pinning to 29

2017-12-27T15:55:43,416 INFO [main] io.druid.guice.JsonConfigurator - Loaded class[class io.druid.server.initialization.ZkPathsConfig] from props[druid.zk.paths.] as [io.druid.server.initialization.ZkPathsConfig@22e2266d]

2017-12-27T15:55:43,460 INFO [main] io.druid.guice.JsonConfigurator - Loaded class[interface io.druid.server.security.Escalator] from props[druid.escalator.] as [io.druid.server.security.NoopEscalator@78422efb]

2017-12-27T15:55:43,480 INFO [main] io.druid.guice.JsonConfigurator - Loaded class[class io.druid.server.security.AuthConfig] from props[druid.auth.] as [AuthConfig{authenticatorChain='null', authorizers='null'}]

Exception in thread "main" com.google.inject.CreationException: Unable to create injector, see the following errors:

1) Problem parsing object at prefix[druid.emitter.kafka]: Instantiation of [simple type, class io.druid.emitter.kafka.KafkaEmitterConfig] value failed: bootstrap.servers can not be null.

  at io.druid.guice.JsonConfigProvider.bind(JsonConfigProvider.java:133) (via modules: com.google.inject.util.Modules$OverrideModule -> io.druid.emitter.kafka.KafkaEmitterModule)

  at io.druid.guice.JsonConfigProvider.bind(JsonConfigProvider.java:133) (via modules: com.google.inject.util.Modules$OverrideModule -> io.druid.emitter.kafka.KafkaEmitterModule)

  while locating com.google.common.base.Supplier<io.druid.emitter.kafka.KafkaEmitterConfig>

  at io.druid.guice.JsonConfigProvider.bind(JsonConfigProvider.java:134) (via modules: com.google.inject.util.Modules$OverrideModule -> io.druid.emitter.kafka.KafkaEmitterModule)

  while locating io.druid.emitter.kafka.KafkaEmitterConfig

    for the 1st parameter of io.druid.emitter.kafka.KafkaEmitterModule.getEmitter(KafkaEmitterModule.java:56)

  at io.druid.emitter.kafka.KafkaEmitterModule.getEmitter(KafkaEmitterModule.java:56) (via modules: com.google.inject.util.Modules$OverrideModule -> io.druid.emitter.kafka.KafkaEmitterModule)

  while locating com.metamx.emitter.core.Emitter annotated with @com.google.inject.name.Named(value=kafka)

  at io.druid.server.emitter.EmitterModule$EmitterProvider.inject(EmitterModule.java:118)

  at io.druid.server.emitter.EmitterModule.configure(EmitterModule.java:78) (via modules: com.google.inject.util.Modules$OverrideModule -> com.google.inject.util.Modules$OverrideModule -> io.druid.server.emitter.EmitterModule)

1 error

        at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:470)

        at com.google.inject.internal.InternalInjectorCreator.injectDynamically(InternalInjectorCreator.java:176)

        at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:110)

        at com.google.inject.Guice.createInjector(Guice.java:99)

        at com.google.inject.Guice.createInjector(Guice.java:73)

        at com.google.inject.Guice.createInjector(Guice.java:62)

        at io.druid.initialization.Initialization.makeInjectorWithModules(Initialization.java:401)

        at io.druid.cli.GuiceRunnable.makeInjector(GuiceRunnable.java:62)

        at io.druid.cli.ServerRunnable.run(ServerRunnable.java:49)

        at io.druid.cli.Main.main(Main.java:108)

Caused by: java.lang.IllegalArgumentException: Instantiation of [simple type, class io.druid.emitter.kafka.KafkaEmitterConfig] value failed: bootstrap.servers can not be null

        at com.fasterxml.jackson.databind.ObjectMapper._convert(ObjectMapper.java:2774)

        at com.fasterxml.jackson.databind.ObjectMapper.convertValue(ObjectMapper.java:2700)

        at io.druid.guice.JsonConfigurator.configurate(JsonConfigurator.java:103)

        at io.druid.guice.JsonConfigProvider.get(JsonConfigProvider.java:200)

        at io.druid.guice.JsonConfigProvider.get(JsonConfigProvider.java:80)

        at com.google.inject.internal.ProviderInternalFactory.provision(ProviderInternalFactory.java:81)

        at com.google.inject.internal.InternalFactoryToInitializableAdapter.provision(InternalFactoryToInitializableAdapter.java:53)

        at com.google.inject.internal.ProviderInternalFactory.circularGet(ProviderInternalFactory.java:61)

        at com.google.inject.internal.InternalFactoryToInitializableAdapter.get(InternalFactoryToInitializableAdapter.java:45)

        at com.google.inject.internal.ProviderToInternalFactoryAdapter$1.call(ProviderToInternalFactoryAdapter.java:46)

        at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1092)

        at com.google.inject.internal.ProviderToInternalFactoryAdapter.get(ProviderToInternalFactoryAdapter.java:40)

        at com.google.inject.internal.SingletonScope$1.get(SingletonScope.java:194)

        at com.google.inject.internal.InternalFactoryToProviderAdapter.get(InternalFactoryToProviderAdapter.java:41)

        at com.google.inject.internal.InjectorImpl$2$1.call(InjectorImpl.java:1019)

        at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1092)

        at com.google.inject.internal.InjectorImpl$2.get(InjectorImpl.java:1015)

        at io.druid.guice.SupplierProvider.get(SupplierProvider.java:52)

        at com.google.inject.internal.ProviderInternalFactory.provision(ProviderInternalFactory.java:81)

        at com.google.inject.internal.InternalFactoryToInitializableAdapter.provision(InternalFactoryToInitializableAdapter.java:53)

        at com.google.inject.internal.ProviderInternalFactory.circularGet(ProviderInternalFactory.java:61)

        at com.google.inject.internal.InternalFactoryToInitializableAdapter.get(InternalFactoryToInitializableAdapter.java:45)

        at com.google.inject.internal.SingleParameterInjector.inject(SingleParameterInjector.java:38)

        at com.google.inject.internal.SingleParameterInjector.getAll(SingleParameterInjector.java:62)

        at com.google.inject.internal.ProviderMethod$Factory.provision(ProviderMethod.java:402)

        at com.google.inject.internal.ProviderMethod$Factory.get(ProviderMethod.java:376)

        at com.google.inject.internal.ProviderToInternalFactoryAdapter$1.call(ProviderToInternalFactoryAdapter.java:46)

        at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1092)

        at com.google.inject.internal.ProviderToInternalFactoryAdapter.get(ProviderToInternalFactoryAdapter.java:40)

        at io.druid.guice.LifecycleScope$1.get(LifecycleScope.java:68)

        at com.google.inject.internal.InternalFactoryToProviderAdapter.get(InternalFactoryToProviderAdapter.java:41)

        at com.google.inject.internal.InjectorImpl$2$1.call(InjectorImpl.java:1019)

        at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1092)

        at com.google.inject.internal.InjectorImpl$2.get(InjectorImpl.java:1015)

        at io.druid.server.emitter.EmitterModule$EmitterProvider.findEmitter(EmitterModule.java:142)

        at io.druid.server.emitter.EmitterModule$EmitterProvider.inject(EmitterModule.java:120)

        at io.druid.server.emitter.EmitterModule$EmitterProvider$$FastClassByGuice$$622b285e.invoke(<generated>)

        at com.google.inject.internal.SingleMethodInjector$1.invoke(SingleMethodInjector.java:54)

        at com.google.inject.internal.SingleMethodInjector.inject(SingleMethodInjector.java:89)

        at com.google.inject.internal.MembersInjectorImpl.injectMembers(MembersInjectorImpl.java:132)

        at com.google.inject.internal.MembersInjectorImpl$1.call(MembersInjectorImpl.java:93)

        at com.google.inject.internal.MembersInjectorImpl$1.call(MembersInjectorImpl.java:80)

        at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1085)

        at com.google.inject.internal.MembersInjectorImpl.injectAndNotify(MembersInjectorImpl.java:80)

        at com.google.inject.internal.Initializer$InjectableReference.get(Initializer.java:223)

        at com.google.inject.internal.Initializer.injectAll(Initializer.java:132)

        at com.google.inject.internal.InternalInjectorCreator.injectDynamically(InternalInjectorCreator.java:174)

        ... 8 more

```