WMS Datastore throws an exception when it can't/won't generate an error message

I'm attempting to cascade a WMS through GeoServer using the WMS Datastore, something is going wrong (which would be fine) however GeoServer is throwing an exception because it doesn't seem to have set the error message. This makes working out what is actually wrong hard.

org.apache.wicket.WicketRuntimeException: Exception 'java.lang.IllegalArgumentException: Value of variable [[error]] could not be resolved while interpolating [[Connection test failed: $

{error}]]' occurred during validation org.geoserver.web.data.store.WMSStoreNewPage$WMSCapabilitiesURLValidator on component 15:form:capabilitiesURL:border:paramValue at org.apache.wicket.markup.html.form.FormComponent.validateValidators(FormComponent.java:1622) at org.apache.wicket.markup.html.form.FormComponent.validate(FormComponent.java:1201) at org.apache.wicket.markup.html.form.Form$23.validate(Form.java:2161) at org.apache.wicket.markup.html.form.Form$ValidationVisitor.formComponent(Form.java:173) at org.apache.wicket.markup.html.form.FormComponent.visitFormComponentsPostOrderHelper(FormComponent.java:441) at org.apache.wicket.markup.html.form.FormComponent.visitFormComponentsPostOrderHelper(FormComponent.java:428) at org.apache.wicket.markup.html.form.FormComponent.visitFormComponentsPostOrderHelper(FormComponent.java:428) at org.apache.wicket.markup.html.form.FormComponent.visitFormComponentsPostOrderHelper(FormComponent.java:428) at org.apache.wicket.markup.html.form.FormComponent.visitFormComponentsPostOrder(FormComponent.java:400) at org.apache.wicket.markup.html.form.Form.visitFormComponentsPostOrder(Form.java:1233) at org.apache.wicket.markup.html.form.Form.validateComponents(Form.java:2153) at org.apache.wicket.markup.html.form.Form.validate(Form.java:2133) at org.apache.wicket.markup.html.form.Form.process(Form.java:1005) at org.apache.wicket.markup.html.form.Form.process(Form.java:955) at org.apache.wicket.markup.html.form.Form.onFormSubmitted(Form.java:920) at org.apache.wicket.ajax.form.AjaxFormSubmitBehavior.onEvent(AjaxFormSubmitBehavior.java:135) at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:177) at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:300) at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:119) at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92) at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250) at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329) at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1436) at org.apache.wicket.RequestCycle.request(RequestCycle.java:545) at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:484) at org.apache.wicket.protocol.http.WicketServlet.doPost(WicketServlet.java:160) at javax.servlet.http.HttpServlet.service(HttpServlet.java:641) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) at org.springframework.web.servlet.mvc.ServletWrappingController.handleRequestInternal(ServletWrappingController.java:158) at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:153) at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:48) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:875) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:809) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:571) at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:511) at javax.servlet.http.HttpServlet.service(HttpServlet.java:641) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.geoserver.filters.ThreadLocalsCleanupFilter.doFilter(ThreadLocalsCleanupFilter.java:23) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.geoserver.filters.SpringDelegatingFilter$Chain.doFilter(SpringDelegatingFilter.java:74) at org.geoserver.filters.SpringDelegatingFilter.doFilter(SpringDelegatingFilter.java:45) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.geoserver.platform.AdvancedDispatchFilter.doFilter(AdvancedDispatchFilter.java:49) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.vfny.geoserver.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:109) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:394) at org.springframework.security.intercept.web.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109) at org.springframework.security.intercept.web.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.ui.ExceptionTranslationFilter.doFilterHttp(ExceptionTranslationFilter.java:101) at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.providers.anonymous.AnonymousProcessingFilter.doFilterHttp(AnonymousProcessingFilter.java:105) at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.ui.rememberme.RememberMeProcessingFilter.doFilterHttp(RememberMeProcessingFilter.java:116) at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.wrapper.SecurityContextHolderAwareRequestFilter.doFilterHttp(SecurityContextHolderAwareRequestFilter.java:91) at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.ui.AbstractProcessingFilter.doFilterHttp(AbstractProcessingFilter.java:278) at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.ui.logout.LogoutFilter.doFilterHttp(LogoutFilter.java:89) at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.context.HttpSessionContextIntegrationFilter.doFilterHttp(HttpSessionContextIntegrationFilter.java:235) at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53) at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:406) at org.springframework.security.util.FilterChainProxy.doFilter(FilterChainProxy.java:185) at org.springframework.security.util.FilterToBeanProxy.doFilter(FilterToBeanProxy.java:99) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.geoserver.filters.LoggingFilter.doFilter(LoggingFilter.java:71) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.geoserver.filters.ReverseProxyFilter.doFilter(ReverseProxyFilter.java:183) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.geoserver.filters.GZIPFilter.doFilter(GZIPFilter.java:41) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.geoserver.filters.SessionDebugFilter.doFilter(SessionDebugFilter.java:46) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565) at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1812) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:662) Caused by: java.lang.IllegalArgumentException: Value of variable [[error]] could not be resolved while interpolating [[Connection test failed: ${error}

]] at org.apache.wicket.util.string.interpolator.VariableInterpolator.toString(VariableInterpolator.java:145) at org.apache.wicket.markup.html.form.FormComponent$MessageSource.substitute(FormComponent.java:233) at org.apache.wicket.validation.ValidationError.getErrorMessage(ValidationError.java:174) at org.apache.wicket.markup.html.form.FormComponent.error(FormComponent.java:677) at org.apache.wicket.markup.html.form.FormComponent$ValidatableAdapter.error(FormComponent.java:337) at org.apache.wicket.validation.validator.AbstractValidator.error(AbstractValidator.java:174) at org.geoserver.web.data.store.WMSStoreNewPage$WMSCapabilitiesURLValidator.onValidate(WMSStoreNewPage.java:97) at org.apache.wicket.validation.validator.AbstractValidator.validate(AbstractValidator.java:81) at org.apache.wicket.markup.html.form.FormComponent.validateValidators(FormComponent.java:1612) ... 106 more