### Environment * Dubbo version: master * Operating System version: 4.9.0-deepin13-amd64 #1 SMP PREEMPT Deepin 4.9.57-1 (2017-10-19) x86_64 GNU/Linux * Java version: 1.8.0_161
### Step to reproduce this issue if i didn't write `<dubbo:consumer client="netty4"></dubbo:consumer>` in `dubbo-demo-consumer.xml`, this program will report an error >https://github.com/apache/incubator-dubbo/tree/master/dubbo-demo/ If there is an exception, please attach the exception trace:  [ Full content available at: https://github.com/apache/incubator-dubbo/issues/2350 ] This message was relayed via gitbox.apache.org for [email protected]
