If you have historical builds without cobertura then the coburtura graph on the
dashboard is broken because of NullPointerException when getting previous
result. I deleted the builds that were done before adding coburtura and the
error went away.

INFO | jvm 1 | 2009/04/02 20:38:20 | 2009-04-02 20:38:20.014::WARN:
/hudson/job/connectfour/cobertura/graph
INFO | jvm 1 | 2009/04/02 20:38:20 | java.lang.NullPointerException
INFO | jvm 1 | 2009/04/02 20:38:20 | at
hudson.plugins.cobertura.CoberturaBuildAction.getPreviousResult(CoberturaBuildAction.java:140)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
hudson.plugins.cobertura.CoberturaBuildAction.getPreviousResult(CoberturaBuildAction.java:125)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
hudson.plugins.cobertura.CoberturaBuildAction.doGraph(CoberturaBuildAction.java:218)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
hudson.plugins.cobertura.CoberturaProjectAction.doGraph(CoberturaProjectAction.java:91)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
sun.reflect.GeneratedMethodAccessor465.invoke(Unknown Source)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
java.lang.reflect.Method.invoke(Method.java:585)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:156)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
org.kohsuke.stapler.Function.bindAndInvoke(Function.java:76)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:73)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
INFO | jvm 1 | 2009/04/02 20:38:20 | at
org.kohsuke.stapler.Stapler.invoke(Stapler.java:436)