title: cannot run jenkins, even after clearing it's directory
body: <p>Tried to upgrade jenkins today. It doesn't start anymore.</p>
  
  <p>Even if i try to remove its directory, it recreates it cleanly but then crashes with following log.</p>
  
  <pre><code>[#|2013-04-24T07:24:49.849+0200|INFO|glassfish3.1.2|javax.enterprise.system.tools.admin.org.glassfish.deployment.admin|_ThreadID=106;_ThreadName=Thread-2;|jenkins was successfully deployed in 3,800 milliseconds.|#]
  
  [#|2013-04-24T07:24:50.100+0200|INFO|glassfish3.1.2|jenkins.InitReactorRunner|_ThreadID=152;_ThreadName=Thread-2;|Listed all plugins|#]
  
  [#|2013-04-24T07:24:50.100+0200|SEVERE|glassfish3.1.2|jenkins.InitReactorRunner|_ThreadID=152;_ThreadName=Thread-2;|Failed Loading plugins
  java.lang.NullPointerException
          at hudson.PluginManager$2$1.run(PluginManager.java:324)
          at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
          at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
          at jenkins.model.Jenkins$7.runTask(Jenkins.java:888)
          at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
          at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
          at java.lang.Thread.run(Thread.java:722)
  |#]
  
  [#|2013-04-24T07:24:50.102+0200|SEVERE|glassfish3.1.2|hudson.WebAppMain|_ThreadID=143;_ThreadName=Thread-2;|Failed to initialize Jenkins
  org.jvnet.hudson.reactor.ReactorException: java.lang.NullPointerException
          at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:246)
          at jenkins.InitReactorRunner.run(InitReactorRunner.java:43)
          at jenkins.model.Jenkins.executeReactor(Jenkins.java:899)
          at jenkins.model.Jenkins.&lt;init&gt;(Jenkins.java:801)
          at hudson.model.Hudson.&lt;init&gt;(Hudson.java:81)
          at hudson.model.Hudson.&lt;init&gt;(Hudson.java:77)
          at hudson.WebAppMain$2.run(WebAppMain.java:214)
  Caused by: java.lang.NullPointerException
          at hudson.PluginManager$2$1.run(PluginManager.java:324)
          at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
          at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
          at jenkins.model.Jenkins$7.runTask(Jenkins.java:888)
          at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
          at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
          at java.lang.Thread.run(Thread.java:722)
  |#]
  </code></pre>
  
  <p>Jenkins 1.512 on Glassfish 3.1.2.2</p>
  
  <p>EDIT: version 1.421 works. Version 1.422 fails. This is consistent, even after wiping jenkins directory.</p>