Symptoms

RSS macro does not work in Confluence and shows this error: java.lang.IllegalArgumentException: Username may not be null, even though the RSS feed does not require a username and password.

Cause

The JVM parameter -Dhttp.auth.ntlm.domain=YourDomain is being used. 

Resolution

Remove the JVM parameter from your JVM setting. Please note that NTLM proxies are supported in version 2.10 or later. See Configuring Web Proxy Support for Confluence.