Error 500 when accessing repository url

HTTP ERROR: 500

INTERNAL_SERVER_ERROR

RequestURI=/archiva/repository/sample/
Caused by:

java.lang.NullPointerException
at org.codehaus.redback.integration.filter.authentication.HttpAuthenticator.authenticate(HttpAuthenticator.java:64)
at org.codehaus.redback.integration.filter.authentication.basic.HttpBasicAuthentication.getAuthenticationResult(HttpBasicAuthentication.java:85)
at org.apache.maven.archiva.webdav.ArchivaDavSessionProvider.attachSession(ArchivaDavSessionProvider.java:66)
at org.apache.maven.archiva.webdav.RepositoryServlet.service(RepositoryServlet.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1093)
at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:413)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:39)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
at org.apache.struts2.dispatcher.ActionContextCleanUp.doFilter(ActionContextCleanUp.java:99)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:360)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:722)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:404)
at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:206)
at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:828)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:514)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:450)

Looks like this is caused by the upgrade to Redback 1.2-beta-2. This doesn't occur in the Archiva 1.2-M1 release.