A dash in XWiki webapp directory causes StringIndexOutOfBounds on save document

To reproduce:

name XWiki folder webapps/test-wiki
start server
create or change document
press "save and continue"

yields error:
java.lang.StringIndexOutOfBoundsException: String index out of range: -1
at java.lang.String.substring(String.java:1932)
at java.lang.String.substring(String.java:1905)
at com.xpn.xwiki.web.ActionFilter.getTargetURL(ActionFilter.java:167)
at com.xpn.xwiki.web.ActionFilter.doFilter(ActionFilter.java:105)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1089)
at com.xpn.xwiki.plugin.webdav.XWikiDavFilter.doFilter(XWikiDavFilter.java:68)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1089)
at com.xpn.xwiki.web.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:295)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1089)
at com.xpn.xwiki.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:112)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1089)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:365)
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:712)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:211)
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:285)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:502)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:835)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:641)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:208)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:378)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:368)
at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:442)

Difficulty:
It ought to be relatively easy to throw an error on startup if the directory name doesn't match [A-Za-z0-9]+
Supporting dashes may be more difficult.