Nginx configuration reverse proxy error occurs

java.lang.IllegalArgumentException: The character [_] is never valid in a domain name.
	at org.apache.tomcat.util.http.parser.HttpParser$DomainParseState.next(HttpParser.java:1048)
	at org.apache.tomcat.util.http.parser.HttpParser.readHostDomainName(HttpParser.java:944)
	at org.apache.tomcat.util.http.parser.Host.parse(Host.java:66)
	at org.apache.tomcat.util.http.parser.Host.parse(Host.java:40)
	at org.apache.coyote.AbstractProcessor.parseHost(AbstractProcessor.java:225)
	at org.apache.coyote.http11.AbstractHttp11Processor.prepareRequest(AbstractHttp11Processor.java:1531)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1112)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:317)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:744)

The reason:
with the "_" character when you configure upstream in nginx configuration file

upstream zp_server1{
        server 127.0.0.1:9999;
    }
	upstream zp_server2{
        server 127.0.0.1:8888;
    }
	upstream zp_server3{
        server 127.0.0.1:8080;
    }
	upstream zp_server4{
        server 127.0.0.1:8686;
    }
	upstream zpserver5{
        server 127.0.0.1:6666;
    }

The "_" removed on the list

After modification, nignx.exe -s reload refresh