对JBMP使用el表达式动态指定申请人出现错误

Struts Problem Report

Struts has detected an unhandled exception:

Messages:

FreeMarker template error!

Method public java.lang.String org.hibernate.exception.NestableRuntimeException.getMessage(int) threw an exception when invoked on org.hibernate.HibernateException: instance not of expected entity type: org.jbpm.pvm.internal.type.variable.UnpersistableVariable is not a: org.jbpm.pvm.internal.type.Variable
The problematic instruction:
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==> ${msgs[0][0]} [on line 76, column 25 in org/apache/struts2/dispatcher/error.ftl]
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Java backtrace for programmers:
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freemarker.template.TemplateModelException: Method public java.lang.String org.hibernate.exception.NestableRuntimeException.getMessage(int) threw an exception when invoked on org.hibernate.HibernateException: instance not of expected entity type: org.jbpm.pvm.internal.type.variable.UnpersistableVariable is not a: org.jbpm.pvm.internal.type.Variable
	at freemarker.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:130)
	at freemarker.ext.beans.SimpleMethodModel.get(SimpleMethodModel.java:138)
	at freemarker.core.DynamicKeyName.dealWithNumericalKey(DynamicKeyName.java:111)
	at freemarker.core.DynamicKeyName._getAsTemplateModel(DynamicKeyName.java:90)
	at freemarker.core.Expression.getAsTemplateModel(Expression.java:89)
	at freemarker.core.Expression.getStringValue(Expression.java:93)
	at freemarker.core.DollarVariable.accept(DollarVariable.java:76)
	at freemarker.core.Environment.visit(Environment.java:221)
	at freemarker.core.MixedContent.accept(MixedContent.java:92)
	at freemarker.core.Environment.visit(Environment.java:221)
	at freemarker.core.IfBlock.accept(IfBlock.java:82)
	at freemarker.core.Environment.visit(Environment.java:221)
	at freemarker.core.IfBlock.accept(IfBlock.java:82)
	at freemarker.core.Environment.visit(Environment.java:221)
	at freemarker.core.MixedContent.accept(MixedContent.java:92)
	at freemarker.core.Environment.visit(Environment.java:221)
	at freemarker.core.Environment.process(Environment.java:199)
	at freemarker.template.Template.process(Template.java:259)
	at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:830)
	at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:534)
	at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
	at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
	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:233)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
	at freemarker.ext.beans.SimpleMemberModel.unwrapArguments(SimpleMemberModel.java:86)
	at freemarker.ext.beans.SimpleMethodModel.exec(SimpleMethodModel.java:106)
	... 37 more
对实体类实现Serializable接口即可