I have a project with two child projects. I'm unable to view the Branches of both child projects. The following error is shown under 'Show Error Detail':

org.apache.wicket.WicketRuntimeException: Error attaching this container for rendering: [WebMarkupContainer [Component id = body]]
	at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1838)
	at org.apache.wicket.Component.onBeforeRender(Component.java:3921)
	at org.apache.wicket.Component.internalBeforeRender(Component.java:950)
	at org.apache.wicket.Component.beforeRender(Component.java:1018)
	at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1826)
	at org.apache.wicket.Component.onBeforeRender(Component.java:3921)
	at io.onedev.server.web.page.project.branches.ProjectBranchesPage$16.onBeforeRender(ProjectBranchesPage.java:705)
	at org.apache.wicket.Component.internalBeforeRender(Component.java:950)
	at org.apache.wicket.Component.beforeRender(Component.java:1018)
	at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1826)
	at org.apache.wicket.Component.onBeforeRender(Component.java:3921)
	at org.apache.wicket.Page.onBeforeRender(Page.java:801)
	at io.onedev.server.web.page.base.BasePage.onBeforeRender(BasePage.java:297)
	at io.onedev.server.web.page.project.branches.ProjectBranchesPage.onBeforeRender(ProjectBranchesPage.java:256)
	at org.apache.wicket.Component.internalBeforeRender(Component.java:950)
	at org.apache.wicket.Component.beforeRender(Component.java:1018)
	at org.apache.wicket.Component.internalPrepareForRender(Component.java:2236)
	at org.apache.wicket.Page.internalPrepareForRender(Page.java:242)
	at org.apache.wicket.Component.render(Component.java:2327)
	at org.apache.wicket.Page.renderPage(Page.java:1018)
	at org.apache.wicket.request.handler.render.WebPageRenderer.renderPage(WebPageRenderer.java:124)
	at org.apache.wicket.request.handler.render.WebPageRenderer.respond(WebPageRenderer.java:236)
	at org.apache.wicket.core.request.handler.RenderPageRequestHandler.respond(RenderPageRequestHandler.java:175)
	at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:917)
	at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64)
	at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:274)
	at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:231)
	at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:302)
	at org.apache.wicket.protocol.ws.AbstractUpgradeFilter.processRequestCycle(AbstractUpgradeFilter.java:70)
	at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:203)
	at org.apache.wicket.protocol.http.WicketServlet.doGet(WicketServlet.java:137)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
	at io.onedev.server.web.DefaultWicketServlet.service(DefaultWicketServlet.java:43)
	at io.onedev.server.web.DefaultWicketServlet$$EnhancerByGuice$$157350596.GUICE$TRAMPOLINE(<generated>)
	at com.google.inject.internal.InterceptorStackCallback$InterceptedMethodInvocation.proceed(InterceptorStackCallback.java:74)
	at io.onedev.server.persistence.SessionInterceptor$1.call(SessionInterceptor.java:23)
	at io.onedev.server.persistence.DefaultSessionManager.call(DefaultSessionManager.java:90)
	at io.onedev.server.persistence.SessionInterceptor.invoke(SessionInterceptor.java:18)
	at com.google.inject.internal.InterceptorStackCallback$InterceptedMethodInvocation.proceed(InterceptorStackCallback.java:75)
	at com.google.inject.internal.InterceptorStackCallback.invoke(InterceptorStackCallback.java:55)
	at io.onedev.server.web.DefaultWicketServlet$$EnhancerByGuice$$157350596.service(<generated>)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:799)
	at org.eclipse.jetty.servlet.ServletHandler$ChainEnd.doFilter(ServletHandler.java:1656)
	at com.google.inject.servlet.DefaultFilterPipeline.dispatch(DefaultFilterPipeline.java:47)
	at com.google.inject.servlet.GuiceFilter.doFilter(GuiceFilter.java:133)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:193)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1626)
	at io.onedev.server.git.GoGetFilter.doFilter(GoGetFilter.java:87)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:193)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1626)
	at io.onedev.server.git.GitLfsFilter.doFilter(GitLfsFilter.java:455)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:193)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1626)
	at io.onedev.server.git.GitFilter.doFilter(GitFilter.java:377)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:193)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1626)
	at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)
	at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
	at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
	at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:154)
	at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
	at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
	at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
	at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:154)
	at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
	at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:458)
	at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:373)
	at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
	at org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
	at org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:387)
	at org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:370)
	at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:154)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:193)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1626)
	at io.onedev.server.jetty.DisableTraceFilter.doFilter(DisableTraceFilter.java:28)
	at org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:193)
	at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1626)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:552)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1624)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1440)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:188)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:505)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1594)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:186)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1355)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.eclipse.jetty.server.handler.gzip.GzipHandler.handle(GzipHandler.java:772)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127)
	at org.eclipse.jetty.server.Server.handle(Server.java:516)
	at org.eclipse.jetty.server.HttpChannel.lambda$handle$1(HttpChannel.java:487)
	at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:732)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:479)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:277)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:311)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:105)
	at org.eclipse.jetty.io.ChannelEndPoint$1.run(ChannelEndPoint.java:104)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:338)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:315)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:173)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:131)
	at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:409)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:883)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1034)
	at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: java.lang.NullPointerException
	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:888)
	at io.onedev.server.web.page.project.branches.ProjectBranchesPage$3.load(ProjectBranchesPage.java:169)
	at io.onedev.server.web.page.project.branches.ProjectBranchesPage$3.load(ProjectBranchesPage.java:161)
	at org.apache.wicket.model.LoadableDetachableModel.getObject(LoadableDetachableModel.java:137)
	at io.onedev.server.web.page.project.branches.ProjectBranchesPage$12.populateItem(ProjectBranchesPage.java:494)
	at org.apache.wicket.extensions.markup.html.repeater.data.grid.AbstractDataGridView.populateItem(AbstractDataGridView.java:156)
	at org.apache.wicket.markup.repeater.RefreshingView$1.newItem(RefreshingView.java:114)
	at org.apache.wicket.markup.repeater.DefaultItemReuseStrategy$1.next(DefaultItemReuseStrategy.java:75)
	at org.apache.wicket.markup.repeater.DefaultItemReuseStrategy$1.next(DefaultItemReuseStrategy.java:56)
	at org.apache.wicket.markup.repeater.RefreshingView.addItems(RefreshingView.java:189)
	at org.apache.wicket.markup.repeater.RefreshingView.onPopulate(RefreshingView.java:97)
	at org.apache.wicket.markup.repeater.AbstractRepeater.onBeforeRender(AbstractRepeater.java:124)
	at org.apache.wicket.markup.repeater.AbstractPageableView.onBeforeRender(AbstractPageableView.java:115)
	at org.apache.wicket.Component.internalBeforeRender(Component.java:950)
	at org.apache.wicket.Component.beforeRender(Component.java:1018)
	at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1826)
	... 106 more