Error while invoking the "insertDefinition" JSP custom tag; see cause exception

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FTL stack trace ("~" means nesting-related):
	- Failed at: @tiles.insertDefinition name="related...  [in template "WEB-INF/fm/detailProduct.ftl" at line 260, column 17]
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Java stack trace (for programmers):
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freemarker.core._TemplateModelException: [... Exception message was already printed; see it above ...]
	at freemarker.ext.jsp.JspTagModelBase.toTemplateModelExceptionOrRethrow(JspTagModelBase.java:154)
	at freemarker.ext.jsp.SimpleTagDirectiveModel.execute(SimpleTagDirectiveModel.java:96)
	at freemarker.core.Environment.visit(Environment.java:389)
	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:104)
	at freemarker.core.Environment.visit(Environment.java:324)
	at freemarker.core.MixedContent.accept(MixedContent.java:54)
	at freemarker.core.Environment.visitByHiddingParent(Environment.java:345)
	at freemarker.core.IfBlock.accept(IfBlock.java:48)
	at freemarker.core.Environment.visit(Environment.java:324)
	at freemarker.core.MixedContent.accept(MixedContent.java:54)
	at freemarker.core.Environment.visit(Environment.java:324)
	at freemarker.core.Environment.process(Environment.java:302)
	at freemarker.template.Template.process(Template.java:325)
	at freemarker.ext.servlet.FreemarkerServlet.process(FreemarkerServlet.java:725)
	at freemarker.ext.servlet.FreemarkerServlet.doGet(FreemarkerServlet.java:642)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:728)
	at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:591)
	at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:527)
	at freemarker.ext.jsp.FreeMarkerPageContext.include(FreeMarkerPageContext.java:385)
	at org.apache.tiles.request.jsp.JspRequest.doInclude(JspRequest.java:123)
	at org.apache.tiles.request.AbstractViewRequest.dispatch(AbstractViewRequest.java:47)
	at org.apache.tiles.request.render.DispatchRenderer.render(DispatchRenderer.java:47)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:259)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:397)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:238)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:221)
	at org.apache.tiles.renderer.DefinitionRenderer.render(DefinitionRenderer.java:59)
	at org.apache.tiles.request.render.ChainedDelegateRenderer.render(ChainedDelegateRenderer.java:68)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:259)
	at org.apache.tiles.template.InsertAttributeModel.renderAttribute(InsertAttributeModel.java:188)
	at org.apache.tiles.template.InsertAttributeModel.execute(InsertAttributeModel.java:132)
	at org.apache.tiles.jsp.taglib.InsertAttributeTag.doTag(InsertAttributeTag.java:299)
	at freemarker.ext.jsp.SimpleTagDirectiveModel.execute(SimpleTagDirectiveModel.java:89)
	at freemarker.core.Environment.visit(Environment.java:389)
	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:104)
	at freemarker.core.Environment.visit(Environment.java:324)
	at freemarker.core.MixedContent.accept(MixedContent.java:54)
	at freemarker.core.Environment.visit(Environment.java:324)
	at freemarker.core.Environment.process(Environment.java:302)
	at freemarker.template.Template.process(Template.java:325)
	at freemarker.ext.servlet.FreemarkerServlet.process(FreemarkerServlet.java:725)
	at freemarker.ext.servlet.FreemarkerServlet.doGet(FreemarkerServlet.java:642)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:728)
	at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:470)
	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:395)
	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:316)
	at org.apache.tiles.request.servlet.ServletRequest.forward(ServletRequest.java:265)
	at org.apache.tiles.request.servlet.ServletRequest.doForward(ServletRequest.java:228)
	at org.apache.tiles.request.AbstractClientRequest.dispatch(AbstractClientRequest.java:57)
	at org.apache.tiles.request.render.DispatchRenderer.render(DispatchRenderer.java:47)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:259)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:397)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:238)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:221)
	at org.apache.tiles.renderer.DefinitionRenderer.render(DefinitionRenderer.java:59)
	at org.springframework.web.servlet.view.tiles3.TilesView.renderMergedOutputModel(TilesView.java:132)
	at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1286)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1041)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:984)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
	at cz.koncepthk.eshop.common.EshopDispatcherServlet.service(EshopDispatcherServlet.java:52)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.orm.hibernate5.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:151)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at cz.koncepthk.eshop.filter.ActionMappingFilter.doFilter(ActionMappingFilter.java:112)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at cz.koncepthk.eshop.filter.AutologinFilter.doFilter(AutologinFilter.java:109)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at cz.koncepthk.eshop.filter.ThreadMaxPriorityFilter.doFilter(ThreadMaxPriorityFilter.java:46)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
	at org.apache.coyote.ajp.AjpProcessor.service(AjpProcessor.java:486)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
	at freemarker.ext.jsp.FreeMarkerPageContext.include(FreeMarkerPageContext.java:385)
	at org.apache.tiles.request.jsp.JspRequest.doInclude(JspRequest.java:123)
	at org.apache.tiles.request.AbstractViewRequest.dispatch(AbstractViewRequest.java:47)
	at org.apache.tiles.request.render.DispatchRenderer.render(DispatchRenderer.java:47)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:259)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:397)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:238)
	at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:221)
	at org.apache.tiles.template.InsertDefinitionModel.renderDefinition(InsertDefinitionModel.java:132)
	at org.apache.tiles.template.InsertDefinitionModel.execute(InsertDefinitionModel.java:99)
	at org.apache.tiles.jsp.taglib.InsertDefinitionTag.doTag(InsertDefinitionTag.java:254)
	at freemarker.ext.jsp.SimpleTagDirectiveModel.execute(SimpleTagDirectiveModel.java:89)
	... 114 more