Please check if the providers have been started and registered.

[byronzoz]

采用consul作为注册中心，服务提供端正常启动，服务调用端报错如下：

waiting for retry, cause: null, dubbo version: 2.7.1, current host: 3.0.1.127 java.lang.NullPointerException at org.apache.dubbo.registry.consul.ConsulRegistry.lambda$convert$3(ConsulRegistry.java:203) at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) at org.apache.dubbo.registry.consul.ConsulRegistry.convert(ConsulRegistry.java:205) at org.apache.dubbo.registry.consul.ConsulRegistry.doSubscribe(ConsulRegistry.java:134) at org.apache.dubbo.registry.support.FailbackRegistry.subscribe(FailbackRegistry.java:290) at org.apache.dubbo.registry.consul.ConsulRegistry.subscribe(ConsulRegistry.java:118) at org.apache.dubbo.registry.integration.RegistryDirectory.subscribe(RegistryDirectory.java:157) at org.apache.dubbo.registry.integration.RegistryProtocol.doRefer(RegistryProtocol.java:386) at org.apache.dubbo.registry.integration.RegistryProtocol.refer(RegistryProtocol.java:367) at org.apache.dubbo.rpc.protocol.ProtocolFilterWrapper.refer(ProtocolFilterWrapper.java:114) at org.apache.dubbo.rpc.protocol.ProtocolListenerWrapper.refer(ProtocolListenerWrapper.java:65) at org.apache.dubbo.qos.protocol.QosProtocolWrapper.refer(QosProtocolWrapper.java:70) at org.apache.dubbo.rpc.Protocol$Adaptive.refer(Protocol$Adaptive.java) at org.apache.dubbo.config.ReferenceConfig.createProxy(ReferenceConfig.java:366) at org.apache.dubbo.config.ReferenceConfig.init(ReferenceConfig.java:305) at org.apache.dubbo.config.ReferenceConfig.get(ReferenceConfig.java:231) at org.apache.dubbo.config.spring.ReferenceBean.getObject(ReferenceBean.java:71) at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:142) at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:102) at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1468) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:249) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194) at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:917) at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:860) at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:775) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:489) at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:286) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1146) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:519) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:296) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:293) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:633) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479) at org.apache.dubbo.container.spring.SpringContainer.start(SpringContainer.java:50) at org.apache.dubbo.container.Main.main(Main.java:89)

切换至ZK作为注册中心，一切正常