NPE because of null references when displaying a document in confluence XHTML syntax

org.apache.velocity.exception.MethodInvocationException: Invocation of method 'displayDocument' in  class com.xpn.xwiki.api.Document threw exception java.lang.NullPointerException: Cannot invoke "org.xwiki.rendering.listener.reference.ResourceReference.clone()" because the return value of "org.xwiki.rendering.block.LinkBlock.getReference()" is null at environment:/templates/contentvars.vm[line 44, column 36]
	at org.apache.velocity.runtime.parser.node.ASTMethod.handleInvocationException(ASTMethod.java:308)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:235)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:368)
	at org.apache.velocity.runtime.parser.node.ASTReference.value(ASTReference.java:704)
	at org.apache.velocity.runtime.parser.node.ASTExpression.value(ASTExpression.java:75)
	at org.apache.velocity.runtime.parser.node.ASTSetDirective.render(ASTSetDirective.java:242)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:190)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
	at org.xwiki.velocity.internal.directive.TryCatchDirective.render(TryCatchDirective.java:86)
	at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:304)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
	at org.apache.velocity.Template.merge(Template.java:358)
	at org.apache.velocity.Template.merge(Template.java:262)
	at org.xwiki.velocity.internal.InternalVelocityEngine.evaluate(InternalVelocityEngine.java:225)
	at com.xpn.xwiki.internal.template.VelocityTemplateEvaluator.evaluateContent(VelocityTemplateEvaluator.java:105)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.evaluateContent(TemplateAsyncRenderer.java:219)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.renderVelocity(TemplateAsyncRenderer.java:174)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:135)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:54)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.lambda$syncRender$0(DefaultAsyncRendererExecutor.java:284)
	at com.xpn.xwiki.internal.security.authorization.DefaultAuthorExecutor.call(DefaultAuthorExecutor.java:98)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.syncRender(DefaultAsyncRendererExecutor.java:284)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.render(DefaultAsyncRendererExecutor.java:267)
	at org.xwiki.rendering.async.internal.block.DefaultBlockAsyncRendererExecutor.render(DefaultBlockAsyncRendererExecutor.java:154)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:904)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:866)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:853)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:808)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:800)
	at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:79)
	at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:73)
	at org.xwiki.template.script.TemplateScriptService.render(TemplateScriptService.java:54)
	at jdk.internal.reflect.GeneratedMethodAccessor3327.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:569)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:571)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:554)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:221)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:368)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:492)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
	at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:218)
	at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:331)
	at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:261)
	at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:304)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
	at org.apache.velocity.Template.merge(Template.java:358)
	at org.apache.velocity.Template.merge(Template.java:262)
	at org.xwiki.velocity.internal.InternalVelocityEngine.evaluate(InternalVelocityEngine.java:225)
	at com.xpn.xwiki.internal.template.VelocityTemplateEvaluator.evaluateContent(VelocityTemplateEvaluator.java:105)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.evaluateContent(TemplateAsyncRenderer.java:219)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.renderVelocity(TemplateAsyncRenderer.java:174)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:135)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:54)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.lambda$syncRender$0(DefaultAsyncRendererExecutor.java:284)
	at com.xpn.xwiki.internal.security.authorization.DefaultAuthorExecutor.call(DefaultAuthorExecutor.java:98)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.syncRender(DefaultAsyncRendererExecutor.java:284)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.render(DefaultAsyncRendererExecutor.java:267)
	at org.xwiki.rendering.async.internal.block.DefaultBlockAsyncRendererExecutor.render(DefaultBlockAsyncRendererExecutor.java:154)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:904)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:866)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:853)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:808)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderNoException(InternalTemplateManager.java:800)
	at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:79)
	at com.xpn.xwiki.internal.template.DefaultTemplateManager.renderNoException(DefaultTemplateManager.java:73)
	at org.xwiki.template.script.TemplateScriptService.render(TemplateScriptService.java:54)
	at jdk.internal.reflect.GeneratedMethodAccessor3327.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:569)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:571)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:554)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:221)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:368)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:492)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
	at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:218)
	at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:331)
	at org.apache.velocity.runtime.directive.RuntimeMacro.render(RuntimeMacro.java:261)
	at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:304)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:171)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:147)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:190)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:439)
	at org.apache.velocity.Template.merge(Template.java:358)
	at org.apache.velocity.Template.merge(Template.java:262)
	at org.xwiki.velocity.internal.InternalVelocityEngine.evaluate(InternalVelocityEngine.java:225)
	at com.xpn.xwiki.internal.template.VelocityTemplateEvaluator.evaluateContent(VelocityTemplateEvaluator.java:105)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.evaluateContent(TemplateAsyncRenderer.java:219)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.renderVelocity(TemplateAsyncRenderer.java:174)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:135)
	at com.xpn.xwiki.internal.template.TemplateAsyncRenderer.render(TemplateAsyncRenderer.java:54)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.lambda$syncRender$0(DefaultAsyncRendererExecutor.java:284)
	at com.xpn.xwiki.internal.security.authorization.DefaultAuthorExecutor.call(DefaultAuthorExecutor.java:98)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.syncRender(DefaultAsyncRendererExecutor.java:284)
	at org.xwiki.rendering.async.internal.DefaultAsyncRendererExecutor.render(DefaultAsyncRendererExecutor.java:267)
	at org.xwiki.rendering.async.internal.block.DefaultBlockAsyncRendererExecutor.render(DefaultBlockAsyncRendererExecutor.java:154)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:904)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:866)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.renderFromSkin(InternalTemplateManager.java:846)
	at com.xpn.xwiki.internal.template.InternalTemplateManager.render(InternalTemplateManager.java:832)
	at com.xpn.xwiki.internal.template.DefaultTemplateManager.render(DefaultTemplateManager.java:91)
	at com.xpn.xwiki.internal.template.DefaultTemplateManager.render(DefaultTemplateManager.java:85)
	at com.xpn.xwiki.XWiki.evaluateTemplate(XWiki.java:2564)
	at com.xpn.xwiki.web.Utils.parseTemplate(Utils.java:180)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:651)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:339)
	at com.xpn.xwiki.web.LegacyActionServlet.service(LegacyActionServlet.java:108)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:590)
	at org.eclipse.jetty.servlet.ServletHolder$NotAsync.service(ServletHolder.java:1419)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:764)
	at org.eclipse.jetty.servlet.ServletHandler$ChainEnd.doFilter(ServletHandler.java:1665)
	at com.xpn.xwiki.web.ActionFilter.doFilter(ActionFilter.java:122)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.xwiki.wysiwyg.filter.ConversionFilter.doFilter(ConversionFilter.java:61)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.xwiki.container.servlet.filters.internal.SetHTTPHeaderFilter.doFilter(SetHTTPHeaderFilter.java:63)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.xwiki.resource.servlet.RoutingFilter.doFilter(RoutingFilter.java:132)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.xwiki.container.servlet.filters.internal.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:208)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.xwiki.container.servlet.filters.internal.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:117)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:210)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.eclipse.jetty.websocket.servlet.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:170)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:527)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:131)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:598)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:223)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1580)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:221)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1384)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:176)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:484)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1553)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:174)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1306)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:129)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:192)
	at org.eclipse.jetty.server.handler.HandlerList.handle(HandlerList.java:51)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122)
	at org.eclipse.jetty.server.Server.handle(Server.java:563)
	at org.eclipse.jetty.server.HttpChannel$RequestDispatchable.dispatch(HttpChannel.java:1598)
	at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:753)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:501)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:287)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:314)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100)
	at org.eclipse.jetty.io.SelectableChannelEndPoint$1.run(SelectableChannelEndPoint.java:53)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.runTask(AdaptiveExecutionStrategy.java:421)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.consumeTask(AdaptiveExecutionStrategy.java:390)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.tryProduce(AdaptiveExecutionStrategy.java:277)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.run(AdaptiveExecutionStrategy.java:199)
	at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:411)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:969)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.doRunJob(QueuedThreadPool.java:1194)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1149)
	at java.base/java.lang.Thread.run(Thread.java:840)
Caused by: java.lang.NullPointerException: Cannot invoke "org.xwiki.rendering.listener.reference.ResourceReference.clone()" because the return value of "org.xwiki.rendering.block.LinkBlock.getReference()" is null
	at org.xwiki.rendering.block.LinkBlock.clone(LinkBlock.java:115)
	at org.xwiki.rendering.block.LinkBlock.clone(LinkBlock.java:37)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:579)
	at org.xwiki.rendering.block.AbstractBlock.clone(AbstractBlock.java:539)
	at org.xwiki.rendering.block.MetaDataBlock.clone(MetaDataBlock.java:101)
	at org.xwiki.rendering.block.XDOM.clone(XDOM.java:122)
	at com.xpn.xwiki.doc.XWikiDocument.getPreparedXDOM(XWikiDocument.java:9000)
	at org.xwiki.display.internal.DocumentContentAsyncExecutor.getPreparedContent(DocumentContentAsyncExecutor.java:135)
	at org.xwiki.display.internal.DocumentContentAsyncExecutor.initialize(DocumentContentAsyncExecutor.java:119)
	at org.xwiki.display.internal.DocumentContentAsyncRenderer.initialize(DocumentContentAsyncRenderer.java:101)
	at org.xwiki.display.internal.DocumentContentDisplayer.display(DocumentContentDisplayer.java:59)
	at org.xwiki.display.internal.DocumentContentDisplayer.display(DocumentContentDisplayer.java:43)
	at org.xwiki.display.internal.DefaultDocumentDisplayer.display(DefaultDocumentDisplayer.java:96)
	at org.xwiki.display.internal.DefaultDocumentDisplayer.display(DefaultDocumentDisplayer.java:39)
	at org.xwiki.sheet.internal.SheetDocumentDisplayer.display(SheetDocumentDisplayer.java:123)
	at org.xwiki.sheet.internal.SheetDocumentDisplayer.display(SheetDocumentDisplayer.java:52)
	at org.xwiki.display.internal.ConfiguredDocumentDisplayer.display(ConfiguredDocumentDisplayer.java:68)
	at org.xwiki.display.internal.ConfiguredDocumentDisplayer.display(ConfiguredDocumentDisplayer.java:42)
	at com.xpn.xwiki.doc.XWikiDocument.display(XWikiDocument.java:1388)
	at com.xpn.xwiki.doc.XWikiDocument.getRenderedContent(XWikiDocument.java:1524)
	at com.xpn.xwiki.doc.XWikiDocument.displayDocument(XWikiDocument.java:1474)
	at com.xpn.xwiki.doc.XWikiDocument.displayDocument(XWikiDocument.java:1443)
	at com.xpn.xwiki.api.Document.displayDocument(Document.java:788)
	at jdk.internal.reflect.GeneratedMethodAccessor3522.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:569)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:571)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:554)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:221)
	... 169 more