Flushing an group that doesn't exist (has never been used) generates a null pointer exception the second time it's called.

My tag is :
<cache:flush group="forum" scope="application"/>

I initially never used this group in the application, and then the second time the page is called, I get the following stack trace.
Just using the group once in my home page seems to resolve the problem ... but what if the home page isn't called first when the webapp reloads ?

Stack trace :

java.lang.NullPointerException
at java.util.HashSet.(HashSet.java:99)
at com.opensymphony.oscache.base.algorithm.AbstractConcurrentReadCache.getGroupForReading(AbstractConcurrentReadCache.java:954)
at com.opensymphony.oscache.base.algorithm.AbstractConcurrentReadCache.getGroup(AbstractConcurrentReadCache.java:372)
at com.opensymphony.oscache.base.Cache.flushGroup(Cache.java:447)
at com.opensymphony.oscache.base.Cache.flushGroup(Cache.java:434)
at com.opensymphony.oscache.web.tag.FlushTag.doStartTag(FlushTag.java:138)
at org.apache.jsp.forum.post_jsp._jspx_meth_cache_flush_0(post_jsp.java:364)
at org.apache.jsp.forum.post_jsp._jspService(post_jsp.java:340)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at com.seanergie.filter.authentication.LoginInterceptorFilter.doFilter(LoginInterceptorFilter.java:36)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at com.seanergie.filter.persistence.SessionsManagerFilter.doFilter(SessionsManagerFilter.java:41)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:407)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:526)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:744)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)

Thanks for your help.

Sylvain.