eShop Error

An error occurred while evaluating custom action attribute "value" with value "${catalog.categoryChildren}": An error occurred while getting property "categoryChildren" from an instance of class ir.cybiran.eshop.client.CatalogHelper
javax.servlet.jsp.JspException: An error occurred while evaluating custom action attribute "value" with value "${catalog.categoryChildren}": An error occurred while getting property "categoryChildren" from an instance of class ir.cybiran.eshop.client.CatalogHelper
	at org.apache.taglibs.standard.lang.jstl.Evaluator.evaluate(Evaluator.java:146)
	at org.apache.taglibs.standard.lang.jstl.Evaluator.evaluate(Evaluator.java:165)
	at org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager.evaluate(ExpressionEvaluatorManager.java:112)
	at org.apache.taglibs.standard.tag.el.core.ExpressionUtil.evalNotNull(ExpressionUtil.java:85)
	at org.apache.taglibs.standard.tag.el.core.SetTag.evaluateExpressions(SetTag.java:147)
	at org.apache.taglibs.standard.tag.el.core.SetTag.doStartTag(SetTag.java:95)
	at org.apache.jsp._4all.default_002dtemplate_jsp._jspx_meth_c_set_6(org.apache.jsp._4all.default_002dtemplate_jsp:420)
	at org.apache.jsp._4all.default_002dtemplate_jsp._jspService(org.apache.jsp._4all.default_002dtemplate_jsp:183)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:672)
	at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:574)
	at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:499)
	at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:966)
	at org.apache.jasper.runtime.PageContextImpl.include(PageContextImpl.java:604)
	at org.apache.struts.taglib.template.InsertTag.doEndTag(InsertTag.java:158)
	at org.apache.jsp.show_jsp._jspx_meth_template_insert_0(org.apache.jsp.show_jsp:140)
	at org.apache.jsp.show_jsp._jspService(org.apache.jsp.show_jsp:94)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
	at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:81)
	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.jboss.web.tomcat.security.CustomPrincipalValve.invoke(CustomPrincipalValve.java:39)
	at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:153)
	at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:59)
	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.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:307)
	at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:385)
	at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:748)
	at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:678)
	at org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:871)
	at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
	at java.lang.Thread.run(Thread.java:722)