The cobertura statistics graphic on a project window isn't rendered. When you
try to load this graphic you get a:

javax.servlet.ServletException: java.lang.NullPointerException
org.kohsuke.stapler.Stapler.invoke(Stapler.java:450)
org.kohsuke.stapler.MetaClass$12.dispatch(MetaClass.java:313)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:438)
org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:181)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:438)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:356)
org.kohsuke.stapler.Stapler.service(Stapler.java:116)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:68)
hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:60)
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)
org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:173)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:42)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:44)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:110)

root cause

java.lang.NullPointerException
hudson.plugins.cobertura.CoberturaBuildAction.getPreviousResult(CoberturaBuildAction.java:140)
hudson.plugins.cobertura.CoberturaBuildAction.getPreviousResult(CoberturaBuildAction.java:125)
hudson.plugins.cobertura.CoberturaBuildAction.doGraph(CoberturaBuildAction.java:218)
hudson.plugins.cobertura.CoberturaProjectAction.doGraph(CoberturaProjectAction.java:91)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:156)
org.kohsuke.stapler.Function.bindAndInvoke(Function.java:76)
org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:73)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:438)
org.kohsuke.stapler.MetaClass$12.dispatch(MetaClass.java:313)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:438)
org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:181)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:438)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:356)
org.kohsuke.stapler.Stapler.service(Stapler.java:116)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:68)
hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:60)
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)
org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:173)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:42)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:55)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:44)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:110)