choose warnings in pipeline snippet generator,

open advanced menu

then click 

jenkins shows NPE error page, debug shows that

WarningsDescriptor.java :93

Ancestor ancestor = request.findAncestor(AbstractProject.class);

ancestor is null , leads following line

if (ancestor.getObject() instanceof AbstractProject) 

crash

full backtrace:

java.lang.NullPointerException at hudson.plugins.warnings.WarningsDescriptor.getDynamic(WarningsDescriptor.java:94) at java.lang.invoke.MethodHandle.invokeWithArguments(Unknown Source) at org.kohsuke.stapler.Function$MethodFunction.invoke(Function.java:343) at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:184) at org.kohsuke.stapler.MetaClass$10.dispatch(MetaClass.java:372) at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:715) Caused: javax.servlet.ServletException at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:765) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:845) at org.kohsuke.stapler.MetaClass$5.doDispatch(MetaClass.java:248) at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58) at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:715) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:845) at org.kohsuke.stapler.MetaClass$10.dispatch(MetaClass.java:374) at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:715) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:845) at org.kohsuke.stapler.MetaClass$5.doDispatch(MetaClass.java:248) at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58) at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:715) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:845) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:649) at org.kohsuke.stapler.Stapler.service(Stapler.java:238) at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:841) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1650) at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:135) at org.jenkinsci.plugins.ssegateway.Endpoint$SSEListenChannelFilter.doFilter(Endpoint.java:225) at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:132) at io.jenkins.blueocean.ResourceCacheControl.doFilter(ResourceCacheControl.java:134) at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:132) at io.jenkins.blueocean.auth.jwt.impl.JwtAuthenticationFilter.doFilter(JwtAuthenticationFilter.java:61) at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:132) at javax.servlet.FilterChain$doFilter.call(Unknown Source) at com.ceilfors.jenkins.plugins.jiratrigger.ExceptionLoggingFilter.doFilter(ExceptionLoggingFilter.groovy:29) at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:132) at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:138) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637) at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:91) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84) at hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87) at jenkins.security.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:117) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87) at org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87) at org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87) at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87) at jenkins.security.BasicHeaderProcessor.doFilter(BasicHeaderProcessor.java:93) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87) at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249) at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87) at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:90) at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:171) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637) at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637) at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:82) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637) at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637) at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:533) at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143) at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:524) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132) at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:190) at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1595) at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188) at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1253) at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:168) at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:473) at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1564) at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:166) at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1155) at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132) at org.eclipse.jetty.server.Server.handle(Server.java:564) at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:317) at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:251) at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279) at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:110) at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124) at org.eclipse.jetty.util.thread.Invocable.invokePreferred(Invocable.java:128) at org.eclipse.jetty.util.thread.Invocable$InvocableExecutor.invoke(Invocable.java:222) at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:294) at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:199) at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)