Java exception when validating page with redirection

Hi, I've installed the CSS validator following this guide:

https://github.com/tlvince/w3c-css-validator-guide

Overall it works fine, but I'm getting a weird java exception when
validating this URL

http://elpais.com/internacional

I get this message:

####################
Target: http://elpais.com/internacional/
java.lang.IllegalArgumentException: protocol = http host = null
####################

And this the error backtrace I see on catalina.out:

#################################################
[ERROR VALIDATOR] http://elpais.com/internacional/
java.lang.IllegalArgumentException: protocol = http host = null
java.lang.IllegalArgumentException: protocol = http host = null
at sun.net.spi.DefaultProxySelector.select(DefaultProxySelector.java:170)
at
sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:925)
at
sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:849)
at org.w3c.css.util.HTTPURL.getConnection(HTTPURL.java:257)
at org.w3c.css.util.HTTPURL.getConnection(HTTPURL.java:276)
at org.w3c.css.util.HTTPURL.getConnection(HTTPURL.java:276)
at org.w3c.css.util.HTTPURL.getConnection(HTTPURL.java:312)
at org.w3c.css.css.DocumentParser.<init>(DocumentParser.java:124)
at org.w3c.css.servlet.CssValidator.doGet(CssValidator.java:363)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
at
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
at
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)
#########################################

I don't see this error on the official validator at
http://jigsaw.w3.org/css-validator/

It looks like it might be caused by the redirection to a different domain.

Any idea how to fix this?

Thanks!

Jaime