Could not find a coercion from type java.lang.String to type epro.db.domain.LotStepInfo.

org.apache.tapestry5.ioc.internal.OperationException: Could not find a coercion from type java.lang.String to type epro.db.domain.LotStepInfo. [at context:lot/LotCreate.tml, line 50]

    at org.apache.tapestry5.ioc.internal.OperationTrackerImpl.logAndRethrow(OperationTrackerImpl.java:121)

    at org.apache.tapestry5.ioc.internal.OperationTrackerImpl.invoke(OperationTrackerImpl.java:88)

    at org.apache.tapestry5.ioc.internal.PerThreadOperationTracker.invoke(PerThreadOperationTracker.java:87)

    at org.apache.tapestry5.ioc.internal.RegistryImpl.invoke(RegistryImpl.java:1124)

    at org.apache.tapestry5.internal.structure.ComponentPageElementResourcesImpl.invoke(ComponentPageElementResourcesImpl.java:146)

    at org.apache.tapestry5.internal.structure.ComponentPageElementImpl.triggerContextEvent(ComponentPageElementImpl.java:1058)

    at org.apache.tapestry5.internal.services.AjaxComponentEventRequestHandler.handle(AjaxComponentEventRequestHandler.java:110)

    at org.apache.tapestry5.internal.services.ajax.AjaxFormUpdateFilter.handle(AjaxFormUpdateFilter.java:56)

    at $ComponentEventRequestHandler_4d773786e4c.handle(Unknown Source)

    at $ComponentEventRequestHandler_4d773786cfc.handle(Unknown Source)

    at org.apache.tapestry5.internal.services.AjaxFilter.handle(AjaxFilter.java:42)

    at $ComponentEventRequestHandler_4d773786cfe.handle(Unknown Source)

    at org.apache.tapestry5.upload.internal.services.UploadExceptionFilter.handle(UploadExceptionFilter.java:75)

    at $ComponentEventRequestHandler_4d773786cfe.handle(Unknown Source)

    at org.apache.tapestry5.services.TapestryModule$41.handle(TapestryModule.java:2476)

    at $ComponentEventRequestHandler_4d773786cfe.handle(Unknown Source)

    at $ComponentEventRequestHandler_4d773786c6e.handle(Unknown Source)

    at org.apache.tapestry5.internal.services.ComponentRequestHandlerTerminator.handleComponentEvent(ComponentRequestHandlerTerminator.java:43)

    at org.apache.tapestry5.services.InitializeActivePageName.handleComponentEvent(InitializeActivePageName.java:39)

    at $ComponentRequestHandler_4d773786c70.handleComponentEvent(Unknown Source)

    at $ComponentRequestHandler_4d773786c40.handleComponentEvent(Unknown Source)

    at org.apache.tapestry5.internal.services.ComponentEventDispatcher.dispatch(ComponentEventDispatcher.java:46)

    at $Dispatcher_4d773786c43.dispatch(Unknown Source)

    at $Dispatcher_4d773786c3d.dispatch(Unknown Source)

    at org.apache.tapestry5.services.TapestryModule$RequestHandlerTerminator.service(TapestryModule.java:302)

    at org.apache.tapestry5.internal.services.RequestErrorFilter.service(RequestErrorFilter.java:26)

    at $RequestHandler_4d773786c3e.service(Unknown Source)

    at org.apache.tapestry5.services.TapestryModule$3.service(TapestryModule.java:902)

    at $RequestHandler_4d773786c3e.service(Unknown Source)

    at org.apache.tapestry5.services.TapestryModule$2.service(TapestryModule.java:892)

    at $RequestHandler_4d773786c3e.service(Unknown Source)

    at org.apache.tapestry5.internal.services.StaticFilesFilter.service(StaticFilesFilter.java:90)

    at $RequestHandler_4d773786c3e.service(Unknown Source)

    at org.apache.tapestry5.internal.services.CheckForUpdatesFilter$2.invoke(CheckForUpdatesFilter.java:105)

    at org.apache.tapestry5.internal.services.CheckForUpdatesFilter$2.invoke(CheckForUpdatesFilter.java:95)

    at org.apache.tapestry5.ioc.internal.util.ConcurrentBarrier.withRead(ConcurrentBarrier.java:85)

    at org.apache.tapestry5.internal.services.CheckForUpdatesFilter.service(CheckForUpdatesFilter.java:119)

    at $RequestHandler_4d773786c3e.service(Unknown Source)

    at $RequestHandler_4d773786c32.service(Unknown Source)

    at org.apache.tapestry5.services.TapestryModule$HttpServletRequestHandlerTerminator.service(TapestryModule.java:253)

    at org.apache.tapestry5.internal.gzip.GZipFilter.service(GZipFilter.java:53)

    at $HttpServletRequestHandler_4d773786c34.service(Unknown Source)

    at org.apache.tapestry5.upload.internal.services.MultipartServletRequestFilter.service(MultipartServletRequestFilter.java:44)

    at $HttpServletRequestHandler_4d773786c34.service(Unknown Source)

    at org.apache.tapestry5.internal.services.IgnoredPathsFilter.service(IgnoredPathsFilter.java:62)

    at $HttpServletRequestFilter_4d773786c30.service(Unknown Source)

    at $HttpServletRequestHandler_4d773786c34.service(Unknown Source)

    at org.apache.tapestry5.services.TapestryModule$1.service(TapestryModule.java:852)

    at $HttpServletRequestHandler_4d773786c34.service(Unknown Source)

    at $HttpServletRequestHandler_4d773786c2e.service(Unknown Source)

    at org.apache.tapestry5.TapestryFilter.doFilter(TapestryFilter.java:171)

    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:298)

    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)

    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)

    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)

    at java.lang.Thread.run(Thread.java:619)

Caused by: org.apache.tapestry5.runtime.ComponentEventException: Could not find a coercion from type java.lang.String to type epro.db.domain.LotStepInfo. [at context:lot/LotCreate.tml, line 50]

    at org.apache.tapestry5.internal.structure.ComponentPageElementImpl.processEventTriggering(ComponentPageElementImpl.java:1141)

    at org.apache.tapestry5.internal.structure.ComponentPageElementImpl.access$3100(ComponentPageElementImpl.java:61)

    at org.apache.tapestry5.internal.structure.ComponentPageElementImpl$5.invoke(ComponentPageElementImpl.java:1062)

    at org.apache.tapestry5.internal.structure.ComponentPageElementImpl$5.invoke(ComponentPageElementImpl.java:1059)
    at org.apache.tapestry5.ioc.internal.OperationTrackerImpl.invoke(OperationTrackerImpl.java:74)

解决方法：有fomr表单的loop 上加个属性  t:formstate="ITERATION"