500 Servlet Exception

java.lang.NullPointerException	at _index__jsp._jspService(/index.jsp:504)	at com.caucho.jsp.JavaPage.service(JavaPage.java:75)	at com.caucho.jsp.Page.subservice(Page.java:506)	at com.caucho.server.http.FilterChainPage.doFilter(FilterChainPage.java:182)	at com.caucho.server.http.Invocation.service(Invocation.java:315)	at com.caucho.server.http.CacheInvocation.service(CacheInvocation.java:135)	at com.caucho.server.http.RunnerRequest.handleRequest(RunnerRequest.java:344)	at com.caucho.server.http.RunnerRequest.handleConnection(RunnerRequest.java:274)	at com.caucho.server.TcpConnection.run(TcpConnection.java:139)	at java.lang.Thread.run(Thread.java:619)