When I drilled down a workspace, I got the following NPE at the one of the
sub-directory.

exception

javax.servlet.ServletException: java.lang.NullPointerException
org.kohsuke.stapler.Stapler.invoke(Stapler.java:425)
org.kohsuke.stapler.MetaClass$9.doDispatch(MetaClass.java:248)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:416)
org.kohsuke.stapler.MetaClass$9.doDispatch(MetaClass.java:248)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:416)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:352)
org.kohsuke.stapler.Stapler.service(Stapler.java:112)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:52)
hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:28)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.ui.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:166)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
hudson.security.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:89)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:44)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:82)

root cause

java.lang.NullPointerException
hudson.model.DirectoryBrowserSupport$ChildPathBuilder.invoke(DirectoryBrowserSupport.java:336)
hudson.model.DirectoryBrowserSupport$ChildPathBuilder.invoke(DirectoryBrowserSupport.java:313)
hudson.FilePath$FileCallableWrapper.call(FilePath.java:1095)
hudson.remoting.UserRequest.perform(UserRequest.java:69)
hudson.remoting.UserRequest.perform(UserRequest.java:23)
hudson.remoting.Request$2.run(Request.java:200)
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:417)
java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:269)
java.util.concurrent.FutureTask.run(FutureTask.java:123)
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
java.lang.Thread.run(Thread.java:595)

It happened on Build 1-200.