Jsf javax.el.ELException:stacktrace中的表达式不能为null

我面临一个问题，页面流按预期工作，但我在控制台上看到stacktrace

[7/10/14 15:26:35:467 IST] 000000e9 lifecycle     W   Expression cannot be null
                             javax.el.ELException: Expression cannot be null
at org.jboss.el.lang.ExpressionBuilder.createNodeInternal(ExpressionBuilder.java:92)
at org.jboss.el.lang.ExpressionBuilder.build(ExpressionBuilder.java:151)
at org.jboss.el.lang.ExpressionBuilder.createValueExpression(ExpressionBuilder.java:195)
at org.jboss.el.ExpressionFactoryImpl.createValueExpression(ExpressionFactoryImpl.java:68)
at javax.faces.application.NavigationCase.getToViewId(NavigationCase.java:264)
at com.sun.faces.application.NavigationHandlerImpl.determineViewFromActionOutcome(NavigationHandlerImpl.java:588)
at com.sun.faces.application.NavigationHandlerImpl.findWildCardMatch(NavigationHandlerImpl.java:400)
at com.sun.faces.application.NavigationHandlerImpl.getViewId(NavigationHandlerImpl.java:282)
at com.sun.faces.application.NavigationHandlerImpl.handleNavigation(NavigationHandlerImpl.java:159)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:129)
at javax.faces.component.UICommand.broadcast(UICommand.java:315)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:792)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1257)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1235)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:779)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:478)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.invokeTarget(WebAppFilterChain.java:136)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:97)
at com.planetj.servlet.filter.compression.CompressingFilter.doFilter(CompressingFilter.java:27

我有一个代码，这似乎是造成问题

try {
            String contextPath = FacesContext.getCurrentInstance().getExternalContext().getRequestContextPath();
            if(contextPath.contains("inside")){
                FacesContext.getCurrentInstance().getExternalContext().redirect("/https.inside"+contextPath+"/view/fees.faces?faces-redirect=true&ER_CONTRACT=" +prefix+contractId);
            }else if(contextPath.contains("employer") || contextPath.contains("tpa"))
                FacesContext.getCurrentInstance().getExternalContext().redirect("https://xyz.local.xyz.com:9443"+contextPath+"/view/fees.faces?faces-redirect=true&contract_num=" +prefix+contractId);
            }   
        catch(IOException e) {
            //Not exception handling
            e.printStackTrace();    
        }

页面正在按预期重定向到url，但stacktrace让我担心

任何帮助都将不胜感激