使用dubbo2.7.5版本时，我同样也出现了这个问题：
```
java.lang.NullPointerException: null
	at org.apache.dubbo.registry.integration.RegistryProtocol.register(RegistryProtocol.java:178) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.registry.integration.RegistryProtocol.export(RegistryProtocol.java:209) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.rpc.protocol.ProtocolListenerWrapper.export(ProtocolListenerWrapper.java:60) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.rpc.protocol.ProtocolFilterWrapper.export(ProtocolFilterWrapper.java:143) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.qos.protocol.QosProtocolWrapper.export(QosProtocolWrapper.java:64) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.rpc.Protocol$Adaptive.export(Protocol$Adaptive.java) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.config.ServiceConfig.doExportUrlsFor1Protocol(ServiceConfig.java:470) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.config.ServiceConfig.doExportUrls(ServiceConfig.java:315) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.config.ServiceConfig.doExport(ServiceConfig.java:287) ~[dubbo-2.7.5.jar:2.7.5]
	at org.apache.dubbo.config.ServiceConfig.export(ServiceConfig.java:205) ~[dubbo-2.7.5.jar:2.7.5]
```
阅读了源码，发现是因为在ServiceRepository类中providers写入提供者信息时没有获取到版本号，写入的Key值也是不带版本号，但是ApplicationModel.getProviderModel(registeredProviderUrl.getServiceKey());获取ProviderModel时，registeredProviderUrl.getServiceKey()是带有版本号值，导致无法从ServiceRepository类中的providers中获取数据而报错。
dubbo以前支持dubbo.provider.version=xxx的方式配置默认版本号，这样就可以不用在xml配置文件或者使用注解时手动指定服务版本。2.7.5版本更新进行改造后该功能缺失引发上述错误，只需要在xml配置文件或使用@Service注解时指定服务版本号version即可。不过还是希望保留该特性以更好的向下兼容。
if (cache == null) {
            cache = ReferenceConfigCache.getCache();
        }
        return cache;
    }
    public DubboBootstrap exportAsync() {
        this.exportAsync = true;
        return this;
    }
    public DubboBootstrap referAsync() {
        this.referAsync = true;
        return this;
    }
    @Deprecated
    public void init() {
        initialize();
    }
    /**
     * Initialize
     */
    private void initialize() {
        if (!initialized.compareAndSet(false, true)) {
            return;
        }
        ApplicationModel.initFrameworkExts();
        startConfigCenter();
        useRegistryAsConfigCenterIfNecessary();
        startMetadataReport();
        loadRemoteConfigs();
        checkGlobalConfigs();