struts2

我把struts2中form表单里的validate设置成true 就出现如下错误 why
FreeMarker template error!Method public java.lang.String com.opensymphony.xwork2.validator.validators.ValidatorSupport.getMessage(java.lang.Object) threw an exception when invoked on com.opensymphony.xwork2.validator.validators.RequiredStringValidator@17d693b
The problematic instruction:
----------
==> ${validator.getMessage(action)?js_string} [on line 50, column 26 in template/xhtml/form-close-validate.ftl]
 in include "/${parameters.templateDir}/xhtml/form-close-validate.ftl" [on line 25, column 1 in template/xhtml/form-close.ftl]
----------Java backtrace for programmers:
----------
freeer.template.TemplateModelException: Method public java.lang.String com.opensymphony.xwork2.validator.validators.ValidatorSupport.getMessage(java.lang.Object) threw an exception when invoked on com.opensymphony.xwork2.validator.validators.RequiredStringValidator@17d693b
at freeer.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:136)
at freeer.core.MethodCall._getAsTemplateModel(MethodCall.java:93)
at freeer.core.Expression.getAsTemplateModel(Expression.java:89)
at freeer.core.Expression.getStringValue(Expression.java:93)
at freeer.core.StringBuiltins$StringBuiltIn._getAsTemplateModel(StringBuiltins.java:71)
at freeer.core.Expression.getAsTemplateModel(Expression.java:89)
at freeer.core.Expression.getStringValue(Expression.java:93)
at freeer.core.DollarVariable.accept(DollarVariable.java:76)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.MixedContent.accept(MixedContent.java:92)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.IteratorBlock$Context.runLoop(IteratorBlock.java:160)
at freeer.core.Environment.visit(Environment.java:351)
at freeer.core.IteratorBlock.accept(IteratorBlock.java:95)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.IteratorBlock$Context.runLoop(IteratorBlock.java:160)
at freeer.core.Environment.visit(Environment.java:351)
at freeer.core.IteratorBlock.accept(IteratorBlock.java:95)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.MixedContent.accept(MixedContent.java:92)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.ConditionalBlock.accept(ConditionalBlock.java:79)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.MixedContent.accept(MixedContent.java:92)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.Environment.include(Environment.java:1375)
at freeer.core.Include.accept(Include.java:155)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.MixedContent.accept(MixedContent.java:92)
at freeer.core.Environment.visit(Environment.java:196)
at freeer.core.Environment.process(Environment.java:176)
at freeer.template.Template.process(Template.java:232)
at org.apache.struts2.components.template.FreeerTemplateEngine.renderTemplate(FreeerTemplateEngine.java:168)
at org.apache.struts2.components.UIBean.mergeTemplate(UIBean.java:530)
at org.apache.struts2.components.UIBean.end(UIBean.java:484)
at org.apache.struts2.views.jsp.ComponentTagSupport.doEndTag(ComponentTagSupport.java:43)
at org.apache.jsp.register2_jsp._jspx_meth_s_005fform_005f0(register2_jsp.java:217)
at org.apache.jsp.register2_jsp._jspService(register2_jsp.java:134)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:384)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:416)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
at com.opensymphony.xwork2.validator.DelegatingValidatorContext$LoggingValidationAware.<init>(DelegatingValidatorContext.java:234)
at com.opensymphony.xwork2.validator.DelegatingValidatorContext.makeValidationAware(DelegatingValidatorContext.java:193)
at com.opensymphony.xwork2.validator.DelegatingValidatorContext.<init>(DelegatingValidatorContext.java:53)
at com.opensymphony.xwork2.validator.validators.ValidatorSupport.getMessage(ValidatorSupport.java:64)
at sun.reflect.GeneratedMethodAccessor71.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at freeer.ext.beans.BeansWrapper.invokeMethod(BeansWrapper.java:616)
at freeer.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:113)
... 58 more