Problème avec le plugin Hudson

J'ai créé presque le même plugin que JobTypeColumn. Il n'y a qu'une seule différence : il affiche la description du poste au lieu du type de poste. Mais après je ne peux pas ajouter cette colonne à ma vue de liste. J'ai une NullPointerException après avoir édité mon config.xml manuellement.

java.lang.NullPointerException
 at hudson.model.Descriptor.newInstancesFromHeteroList(Descriptor.java:626)
 at hudson.util.DescribableList.rebuildHetero(DescribableList.java:164)
 at hudson.model.ListView.submit(ListView.java:262)
 at hudson.model.View.doConfigSubmit(View.java:484)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
 at java.lang.reflect.Method.invoke(Unknown Source)
 at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:185)
 at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:101)
 at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:54)
 at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:74)
 at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
 at org.kohsuke.stapler.Stapler.invoke(Stapler.java:492)
 at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:180)
 at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
 at org.kohsuke.stapler.Stapler.invoke(Stapler.java:492)
 at org.kohsuke.stapler.Stapler.invoke(Stapler.java:408)
 at org.kohsuke.stapler.Stapler.service(Stapler.java:117)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:45)
 at winstone.ServletConfiguration.execute(ServletConfiguration.java:249)
 at winstone.RequestDispatcher.forward(RequestDispatcher.java:335)
 at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:378)
 at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:94)
 at net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:304)
 at org.jvnet.hudson.plugins.monitoring.HudsonMonitoringFilter.doFilter(HudsonMonitoringFilter.java:31)
 at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:97)
 at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:86)
 at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
 at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
 at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:47)
 at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
 at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
 at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
 at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
 at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
 at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
 at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
 at winstone.RequestDispatcher.forward(RequestDispatcher.java:333)
 at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:244)
 at winstone.RequestHandlerThread.run(RequestHandlerThread.java:150)
 at java.lang.Thread.run(Unknown Source)