- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.6-SNAPSHOT(current master branch)
* Operating System version: mac os
* Java version: 1.8

### Steps to reproduce this issue

1. config nacos as register and metadata center as following
    <dubbo:registry address="nacos://127.0.0.1:8848"/>
    <dubbo:metadata-report address="nacos://127.0.0.1:8848"/>

2. run Application in dubbo-demo-xml-provider and bug occurs
[19/01/20 22:59:10:949 CST] main  WARN metadata.DynamicConfigurationServiceNameMapping:  [DUBBO] timeouts can't be negative, dubbo version: , current host: ***.***.***.***

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

What do you expected from the above steps？

Metadata are published to nacos

### Actual Result

What actually happens?

Publish failed with this bug
Just put your stack trace here!
```
java.lang.IllegalArgumentException: timeouts can't be negative
	at sun.net.www.protocol.http.HttpURLConnection.setReadTimeout(HttpURLConnection.java:3231)
	at com.alibaba.nacos.client.config.impl.HttpSimpleClient.httpGet(HttpSimpleClient.java:59)
	at com.alibaba.nacos.client.config.http.ServerHttpAgent.httpGet(ServerHttpAgent.java:80)
	at com.alibaba.nacos.client.config.http.MetricsHttpAgent.httpGet(MetricsHttpAgent.java:48)
	at com.alibaba.nacos.client.config.impl.ClientWorker.getServerConfig(ClientWorker.java:234)
	at com.alibaba.nacos.client.config.NacosConfigService.getConfigInner(NacosConfigService.java:173)
	at com.alibaba.nacos.client.config.NacosConfigService.getConfig(NacosConfigService.java:122)
	at org.apache.dubbo.configcenter.support.nacos.NacosDynamicConfiguration.publishConfig(NacosDynamicConfiguration.java:263)
	at org.apache.dubbo.common.config.configcenter.wrapper.CompositeDynamicConfiguration.publishConfig(CompositeDynamicConfiguration.java:72)
	at org.apache.dubbo.metadata.DynamicConfigurationServiceNameMapping.lambda$map$0(DynamicConfigurationServiceNameMapping.java:59)
	at org.apache.dubbo.metadata.DynamicConfigurationServiceNameMapping.execute(DynamicConfigurationServiceNameMapping.java:92)
	at org.apache.dubbo.metadata.DynamicConfigurationServiceNameMapping.map(DynamicConfigurationServiceNameMapping.java:58)
	at org.apache.dubbo.config.event.listener.ServiceNameMappingListener.lambda$onEvent$0(ServiceNameMappingListener.java:52)
	at java.util.ArrayList.forEach(ArrayList.java:1257)
	at org.apache.dubbo.config.event.listener.ServiceNameMappingListener.onEvent(ServiceNameMappingListener.java:47)
	at org.apache.dubbo.config.event.listener.ServiceNameMappingListener.onEvent(ServiceNameMappingListener.java:39)
	at org.apache.dubbo.event.AbstractEventDispatcher.lambda$null$5(AbstractEventDispatcher.java:130)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
	at java.util.ArrayList.forEach(ArrayList.java:1257)
	at java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:390)
	at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
	at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
	at org.apache.dubbo.event.AbstractEventDispatcher.lambda$dispatch$6(AbstractEventDispatcher.java:122)
	at org.apache.dubbo.event.AbstractEventDispatcher.dispatch(AbstractEventDispatcher.java:120)
	at org.apache.dubbo.config.ServiceConfig.dispatch(ServiceConfig.java:704)
	at org.apache.dubbo.config.ServiceConfig.doExport(ServiceConfig.java:295)
	at org.apache.dubbo.config.ServiceConfig.export(ServiceConfig.java:205)
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.lambda$exportServices$13(DubboBootstrap.java:876)
	at java.util.HashMap$Values.forEach(HashMap.java:981)
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.exportServices(DubboBootstrap.java:864)
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.start(DubboBootstrap.java:706)
	at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onContextRefreshedEvent(DubboBootstrapApplicationListener.java:52)
	at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onApplicationContextEvent(DubboBootstrapApplicationListener.java:45)
	at org.apache.dubbo.config.spring.context.OneTimeExecutionApplicationContextEventListener.onApplicationEvent(OneTimeExecutionApplicationContextEventListener.java:40)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:393)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:347)
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:883)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:546)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
	at org.apache.dubbo.demo.provider.Application.main(Application.java:23)
throw new IllegalStateException(e);
        }
        return configService;
    }
    private HttpAgent getHttpAgent(ConfigService configService) {
        HttpAgent agent = null;
        try {
            Field field = configService.getClass().getDeclaredField("agent");
            field.setAccessible(true);
            agent = (HttpAgent) field.get(configService);
        } catch (Exception e) {
            throw new IllegalStateException(e);
        }
        return agent;
    }
    private Properties buildNacosProperties(URL url) {
        Properties properties = new Properties();
        setServerAddr(url, properties);
        setProperties(url, properties);
        return properties;
    }
    private void setServerAddr(URL url, Properties properties) {
        StringBuilder serverAddrBuilder =
                new StringBuilder(url.getHost()) 
                        .append(":")
                        .append(url.getPort()); 
        
        String backup = url.getParameter(BACKUP_KEY);
        if (backup != null) {
            serverAddrBuilder.append(",").append(backup);